Reiny
Popular questions and responses by Reiny
Happy Pi Day
Happy Pi Day to all math "nerds" Even Google changed their log today. http://www.squidoo.com/PiDay
asked on March 14, 2010 
Ms. Sue , we will miss you
Ms. Sue was a kind, gentle, and good person that I had the privilege of knowing through this webpage. I have been a tutor for about 12 years on here, and was always impressed by the patient and competent way she helped students. You will be missed Reiny
asked on December 10, 2019 
@Peter, earlier question
Peter, I found your question interesting and have been messing with it for a while www.jiskha.com/questions/1789041/Ethelwenttothefarmersmarkettobuysomeeggsnotinadozencartonsonthe I finally made up a short computer program using a silly old
asked on March 19, 2019 
FOR NABIAH
You now have 6 different posts going for the same "cake question" I am not going to keep going back to see which one you replied to. Stay with one posting please. I just notice one way down the list where you did part a) Calculate the area on top of the
asked on April 22, 2010 
Algebra
3(2+32(45)21)3(2+4(42)8+3(25)+12)13)+45 rather silly question, and some of it makes no sense eg look at the first part ......2(45)21 does this end up 2(1)(2) ? or did you forget an operator before the last 2? there is a similar discrepancy
asked on August 21, 2007 
@ Steve or Damon
take a look at this question http://www.jiskha.com/display.cgi?id=1446147947 Am I guilty of overkill or overthinking this ? Surely there has to be an easier way.
asked on October 29, 2015 
For Anubhav
re http://www.jiskha.com/display.cgi?id=1368707176 I have a solution, but what a mess. Before I type it all out, let me know if you still need the solution. I certainly don't feel like typing it all out unless you will actually look at it.
asked on May 16, 2013 
for Knights
have been looking at your post ... http://www.jiskha.com/display.cgi?id=1357047578 interesting question... let the altitude of 12 hit base a let the altitude of 14 hit base b then (1/2)(12)a = (1/2)(14)b 6a = 7b a = 7b/6 let the third side be c and its
asked on January 1, 2013 
For Lia  question from this morning
I took some time to work out your rather "nasty" Calculus question. Take a look at it and see if it matches your expected result. http://www.jiskha.com/display.cgi?id=1300878253
asked on March 23, 2011 
To Math Students, re √ sign
Several student tonight have asked me how I create the √ symbol to create √ symbol on a PC, hold down the Alt key, and at the same time press 251 on the number pad, then release the Alt key on Mac, hold down the Option key, and press V, release the
asked on June 9, 2010 
For <b>marie flore joseph</b>
Please do not add your new question as a response to somebody else's post. click on "Post a New Question" above to post your problem. Here is your question : Math  marie flore joseph, Monday, April 5, 2010 at 10:37pm the difference of the squares of two
asked on April 5, 2010 
For Haley
Even though you mean well, your last three responses have been either incomplete or incorrect. The one to http://www.jiskha.com/display.cgi?id=1258225501 is totally off the mark. Please make sure you are familiar with the topic before replying.
asked on November 14, 2009 
For MUFFY
You stated on Saturday that you understood my solution as far as part a) and b) were, so let me just recap what we did. (I will not repeat the actual question) My Solution: Suppose we label the point of contact P(x,y). I bet P is in the first quadrant. but
asked on October 5, 2009 
Nice unanswered question by Maggie
"100 bushels of corn are divided among 100 men, women, and children. Men receive 3 bushels each, women 2 bushels and children 1/2 bushel each. How can the bushels be distributed? is there more than one solution? if so, find the other solutions." let the
asked on September 16, 2009 
Reiny to Gina (logic)
I saw your reply re my late night solution to your pumpkin question http://www.jiskha.com/display.cgi?id=1224212047 I did indeed make two typing errors, which even though they do not change the actual answer, nevertheless would have caused confusion. I
asked on October 17, 2008 
For George
At 11:37 and at 12:24 you posted the same question the earlier one was answered correctly by drwls by accepting your question the way you typed it. my solution is based on the assumption that your denominator was e^(t7), an invalid assumption.
asked on September 11, 2008 
math.algebra
other than factoring out the 9 there is really no simplification that can be made here 9sqrt6  9sqrt2 =9(√6  √2) can someone help me simplify: 9sqrt6  9sqrt2
asked on July 29, 2007 
college Algebra
This is "college" math? Anyway... let the smaller number be x, and the larger number be x+8 then x + x+8 < 12 this is easy to solve, let me know what you got. the sum of two numbers is less than 12. The second number is 8 more than the first.what are the
asked on July 25, 2007 
maths
Set it up this way: Let the number of students be x let the number of rows be y then the number of students per row is x/y This results in 2 equations from your data: (x/y+1)(y2) = x and (x/y1)(y+3 = x Solve these two, gets a bit messy at first but it
asked on July 15, 2007 
algebra
These are very easy to set up with a "chart" DistanceRateTime (D=RxT) slow way 6xx6 fast way  5(x+7)x+75 so 6x = 5(x+7) 6x=5x+35+ x=35 The speed on the slower trip was 35 mph, and on the return trip 42 mph A
asked on June 17, 2007 
math
break it down into cases at most one day of rain in 3 days to me means we could have: norain norain norain > (1/3)^3 = 1/27 rain norain norain > 2/3(1/3^2 = 2/27 norain rain norain > same as above = 2/27 norain norain rain > same
asked on May 17, 2007 
I can write it instead
Leo, a similar prediction is often made about arithmetic since the invention of the calculator. in one of Isaac Asimov writings they discover a man who is actually able to perform an operation like 368 x 4821 with something called a pencil and paper. My
asked on May 15, 2007 
math
You did not watch your units, you are mixing inches and feet Your equation should have been 1/2 = 1/di + 1/120 (I changed 10 feet to 120 in) solve this for di and you get 2.03 inches. Please help me I am so confused I think I am losing my mind. The focal
asked on May 9, 2007 
Vectorsanother angle confusion
On an xy grid, label them NS, EW, draw a line from the origin to the right and label it 425 (you are going East) From the end of that line draw a vertical line upwards of 40 (you are going North) Use an approximate scale, realizing that 425 is just
asked on April 20, 2007 
Vectors
I hope that the diagram I have drawn for myself matches the one in your question. I have a triangle with sides 20 and 10 and an angle of 120º between them By the cosine law I found the third side to be 26.4575. You said you found the maginitude, I hope we
asked on April 20, 2007 
Trig
I don't know the physics behind Snell's Law, but I can do the math Snell's Law says sin(angle of incidence)/sin(angle of reflection) = refractive index since you know the two angles... sin45/sin27 = refractive index =1.5575365 so for an angle of refection
asked on April 19, 2007 
help, bobpursely
Please take a look at DEVON's trig equation at 9:14 I must be missing something obvious. If the second had been 3sin 2x it would be a straight forward question. The way it stands I was able to "reduce" it to the equation 8sin^4 x  8sin^2 x + 3sin x + 2 =
asked on April 16, 2007 
math
how about (53)x2 + 8(52) ? To me these are really just "puzzles" and do not actually require much mathematical ability. The best and often only way is to by 'trial and error'. what is the rule when grouping numbers? example I want the answer to be 28. 5
asked on March 28, 2007 
algebra
I trust you know about y = mx + b Realize that when you are given the x or y intercepts, you are really just given two points, in your case the points (4,0) and (0,2) So it is easy to find the slope, (20)/(04) = 1/2 Take it from there Determine the
asked on March 28, 2007 
algrbra
Complimentary angles add up to 90º So translate the English into Math. if you let the unknown angle be x then "the measure of the compliment of the angle" > 90x "10 degrees less than three times the measure of the angle" > 3x  10 so....... 90x
asked on March 28, 2007 
principles of finances
according to my interpretation of the question in October they would collect: the 10% of the August sales = .10($10,000) the 20% of the Sept sales = .20($20,000) and the 70% of the Oct sales = .70($30,000) Do the arithmetic and add them up A project has an
asked on March 28, 2007 
calc
I assume the poster was trying to type "oblique asymptote" from your answer of 3x+2 + 7/(x1) we can conclude that there is an oblique linear asymptote of y = 3x + 2, and a vertical asymptote at x = 1 for the original function given. how do u find obblique
asked on March 26, 2007 
Monitors of Board
Is there any way that the postings could be numbered? The post below this one by TONY obviously refers to a previous posting of his 8 steps below. I know the URL has a number behind each particular post, and each post can be identified by a title and
asked on March 20, 2007 
factoring
let f(m)=m^3 + 3m^2 + 3m + 1 notice f(1) = 0, so m+1 is a factor. Using division, the answer is m^2 + 2m + 1 which factors once more to (m+1)(m+1) so you have (m+1)^3 = 0 and then m = 1 Are you familiar with Pascal's triangle? Did you notice the pattern
asked on March 11, 2007 
math
There is no function equation for the Fibonacci numbers, you have to use a Recursion formula. F(n) = F(n1) + F(n2) for n>2 and F(1)=1, F(2)=1 what is the equation for the fibonacci sequence
asked on March 11, 2007

Math
mean number of hours  x hours worked the first 8 days = 8x hours worked the last 2 days = 2(x+2) 8x + 2(x+2) = 69 10x = 65 x = 6.5 So the last 2 days he worked 2(6.5+2) = 17 hours check: hours worked the first 8 days = 8x = 8(6.5) = 52 and 52+17 = 69
posted on August 7, 2020 
Algebra 2
(24x^9+3x^3)(7x+x^36+12x^4) = 2  4x^9 + 3x^3  7x  x^3 + 6  12x^4 = 4x^9 + 12x^4 + 2x^3  7x + 8
posted on August 7, 2020 
math
There is no "equation" to solve if you want to evaluate "3 x seven tenths" = 3(7/10) = 21/10 or 2.1
posted on August 6, 2020 
Mathematics
number of single digits without a 6 = 8 number of double digits without a 6 = 8*9 = 72 number of triple digits without a 6 = 1 number without a 6 = 81 so number containing a 6 = 10081 = 19
posted on August 6, 2020 
math
oops, pressed "submit" too soon , forgot to raise that boat: height = .9sin(π/2 t) + .9 b) .9sin(π/2 t) + .9 > ?? ( is the normal position the water level, that is , zero or is it 0.9 ? You decide, you will get 2 answers.)
posted on August 6, 2020 
math
So clearly the amplitude is .9 m 2π/k = period 2π/k = 4 4k = 2π k = π/2 but we want the low point to be 0 not .9 so height = .9sin(π/2 t), where t is in seconds and height is in metres
posted on August 6, 2020 
mathematics
what's with the � ?? anyway, if you expand this you will get a trinomial after simplifying.
posted on August 6, 2020 
mathematics
together on the first day they earned x + 4x+7 = 5x +7 they did this for 3 days, so what is 3(5x+7) ?
posted on August 6, 2020 
math
the range is 62 = 4 so the amplitude is 2 normally, the minimum would be 2 , but it is +2, so the vertical shift must be +4
posted on August 6, 2020 
mathematics
present time: Alice  a Beatrice  b 10 years ago: a10 + b10 = 21 a+b = 41 ** in 8 year's time: a+8 = 2(b+8) a+8 = 2b + 16 a  2b = 8 *** subtract *** from ** 3b = 33 b = 11 , then a = 30 State your conclusions
posted on August 5, 2020 
Mathematics
I will assume you meant 2√3 to be the base, that is, you want log
posted on August 5, 2020 
mathematics
Aren't you just going in the "opposite" direction? what is 127.5 + 180 ?
posted on August 5, 2020 
mathematics
6 + 6 ÷ 6 x 6  6 = 6 + (6 ÷ 6 x 6)  6 = 6 + (1 x 6)  6 = 6 + 6  6 = 6
posted on August 5, 2020 
Trigonometry
Are we solving? cot Ø = 1 or tanØ = 1 angle in standard position is 45° or π/4 rads the tangent is positive in I or III Ø = 45° or 225° or Ø = π/4 or 5π/4
posted on August 5, 2020 
mathematics
I have triangle PQR, with angle P = 60° and RP = 10 not enough information.
posted on August 4, 2020 
Math
addition: **0 1 2 3 0 0 1 2 3 1 1 2 3 10 2 2 3 10 11 3 3 10 11 12 e.g. 2 + 3 = 11 multiplication: ** 1 2 3
posted on August 4, 2020 
Math
You didn't actually ask a question. I will assume you want to know how the profit of ₹61,500 must be distributed, and I will assume that the rate is 18% per annum, compounded monthly and will be applied to all monies. At end of year, value of Ram's
posted on August 4, 2020 
mathematics
Looks like a GP, with a = 2 and r = 3 Which term number is 1458 ? ar^(n1) = 1458 2(3^(n1)) = 1458 3^(n1) = 729 , but I know 3^6 = 729 so n1 = 6 and n = 7 so now you want sum(7) = 2(3^7  1)/(31) = ...
posted on August 4, 2020 
Maths
The traditional way to do this style of question has you ending up with height = 8*tan32*tan43/(tan43  tan32) = .... I found through the years that students follow more readily the following method: Label the top of the tower P and its bottom Q label the
posted on August 3, 2020 
mathematics
remaining balance (present value of the loan) = .85(600) = 510 let the weekly rate be i, expressed as a decimal then 22(1  (1+i)^25)/i = 510 very nasty equation to solve, we need some "tools", let's use Wolfram
posted on August 3, 2020 
Maths
.9x = 135 solve for x
posted on August 3, 2020 
math
Make a treediagram, two main brances as R and NR , (red and nonred) each of those has subbrances of F and NF place the probabilities on each branch you have 4 possible outcomes RF = (1/4)(3/4) = 3/16 RNR = (1/4)(1/4) = 1/16 NRF = (3/4)(1/16) = 3/64
posted on August 3, 2020 
Mathematics
Possible outcomes: V V > (5/26)(5/26) = 25/676 V C > (5/26)(21/26) = 105/676 C V >(21/26)(5/26) = 105/676 C C > (21/26)(21/26) = 441/676 , notice the sum is 1 E(x) = 6(25/676) + 3(105/676) + 3(105/676) + 0(441/676) = ....
posted on August 3, 2020 
geometry
Type it this way: y^2 / 1096  x^2 / 41334 = 1 or x^2/41334  y^2/1096 = 1 So you have a vertical hyperbola Using your properties of a hyperbola x^2/a^2  y^2/b^2 = 1 we know that c^2 = a^2 + b^2 c^2 = 41334 + 1096 = 42430 c = √42430 = appr 205.98 and
posted on August 3, 2020 
maths
Yes, since 1/10 + 1/5 + 3/5 = 9/10 which is not equal to 1 so the prob of selecting the other colour(s), there could be more than one other, is 1/10
posted on August 3, 2020 
Mathematics
a + ar = 3 > a(1+r) = 3 ar + ar^2 = 6 > ar(1+r) = 6 divide the 2nd equation by the first r = 2 now sub that into the first to get a and you are all set
posted on August 3, 2020 
maths
We could start by defining karla's age ... let karla's age be x years then ama is x+3 daniel is x+2 + 2 = x+5 x + x+3 + x+5 = 32 solve for x, then sub into my definitions
posted on August 2, 2020 
Algebra
Let's start with some common sense. 17 has to be the sum of two powers The only "powers" ≤ 17 are 1, 4, 8, 9, and 16 well, 8 + 9 = 17 2^3 + 3^2 = 17, and sure enough 2+3 = 5 so x = 2, y = 3, or x = 3, y = 2 are solutions the graph of x^y + y^x = 17 looks
posted on August 1, 2020 
Maths
Unit price for A : 1.30/800 = .. Unit price for B : 2.30/1500 = ... What do you think?
posted on August 1, 2020 
mathematics
Perhaps one step further ... ln((3x  5)^1/2)  ln(7) = (1/2) ln(3x5)  ln 7
posted on August 1, 2020 
Mathematics
Look at the original lines first. https://www.wolframalpha.com/input/?i=graph+y2x%3D3%2C+2yx%3D9 As you can see, there would be two such lines, one will have a positive slope, the other will have a negative slope. To be on the axis of symmetry, any point
posted on August 1, 2020 
math
In a rightangled triangle the hypotenuse must be the longest side. Check your question.
posted on July 31, 2020 
Finance
same type again
posted on July 31, 2020 
Finance
same thing Let me know what you get
posted on July 31, 2020 
Finance
Nobody uses "tables" any more, this is 2020 8% interest compounded quarterly > rate is .02 per quarter 6 year = 24 quarter years x(1.02)^24 = 24000 This is the same type of question as your previous post
posted on July 31, 2020 
Finance
2.19% compounded daily  daily rate = .0219/365 = .00006 per day number of days in 4 years = 1460 x(1.00006)^1460 = 33,000 x = 33000/(1.00006)^1460 = 30,232.28
posted on July 31, 2020 
mathematics
Sept deposit  x Oct deposit  2x Nov deposit  (1/2)x or x/2 total (ignoring any interest involved) = x +2x + x/2 = (2x + 4x + x)/2 = 7x/2 or 3.5x or (7/2)x
posted on July 30, 2020 
mathematics
side^2 = 169 side = √169 = ...
posted on July 30, 2020 
mathematics
√8105 = 90.02... so 90^2 or 8100 would be the previous perfect square, So what must you do to 8105 to get to it ?
posted on July 30, 2020 
mathematics
Why did this remind me of an old TV show by Roy Underhill, called The Woodwright's Shop? They did woodworking using only vintage, musclepowered and handtools.
posted on July 30, 2020 
mathematics
Let the plane's position be labelled A, and the bottom of the vertical B In triangle APR, angle A = 30° using basic geometry. Then PR = AR = 15, since we now have an isosceles triangle. then sin60° = AB/AR AB = 15sin60 = appr 12.99 or 13 metres
posted on July 29, 2020 
math
Dan 's marbles  x Leah's marbles  x+28 (1/3)(x+28) = (4/5)x times 15 5(x+28) = 12x solve for x , then sub into Leah's marbles
posted on July 29, 2020 
math
f(x) = x+2 g(x) = (x3)^2 The only difficult one is the first: g(f(x)) = g(x+2) = (x+2  3)^2 = (x1)^2 or x^2 + 2x + 1 for the second, just add the two expressions for the third, just multiply the two expressions
posted on July 29, 2020 
Math
In any triangle, the sum of two sides must be greater than the third side xcm, (x +3)cm and 10 x + x+3 > 10 > x > 3.5 x + 10 > x+3 > 10 > 3 , which is true x+3 + 10 > x > 13 > 0 , yup, true also so x > 3.5 But x is supposed to be a whole number,
posted on July 29, 2020 
Math
Do you have a question? If x+3 > 10 then x > 7 if x+3 < 10 then x < 7 That should cover it
posted on July 29, 2020 
Mathematics
Use / as your division sign, enclose numerators and denominators in brackets. e.g. cos x−sin x _ __________ 4 cos x+sin x could mean: cosx/4  sinx/(cosx + sinx) I will assume that is what you meant. given tanx = 3 = 3/1 = y/x , so make a sketch of your
posted on July 29, 2020 
Mathematics
n : d = 2:3 = 16 : 24 d : bills = 8:1 = 24 : 3 n : d : bills = 16:24:3 coins : bills = (16+24) : 3 = 40 : 3
posted on July 28, 2020 
Mathematics
Duhh, R_scott, you are right, and I even told them to make a sketch.
posted on July 28, 2020 
Math
Or the wonderful and powerful Wolfram https://www.wolframalpha.com/input/?i=23897923%5E3
posted on July 28, 2020 
Mathematics
Only the middle piece of the 6 edges have two sides painted, the corners have 3 sides painted Make yourself a rough sketch to see that. So there would be 6, but that is not one of the given choices, so, none of the above
posted on July 28, 2020 
Geometry
Oh my, somebody seriously has to review the basic trig ratios to find that sinA = 13/15 A = arcsin(13/15) = .... on my calculator I did 13 ÷ 15 = ... 2ndF sin = ... or I could have done 2ndF (13÷15) =
posted on July 27, 2020 
algebra
larger  x smaller  y xy = 16 xy = 23 x^2 + y^2 = (x  y)^2 + 2xy = 16^2 + 46 = 302
posted on July 27, 2020 
Mathematics
NOW: Melissa  x Laura  2x Kim  2x+10 x+5 = 10 x = 5 So Kim is 2x+10 = 10+10 = 20
posted on July 27, 2020 
Mathematics
pressed too soon, but I am sure you can state the GP.
posted on July 27, 2020 
Mathematics
I will read that as: the product of the 2nd and the 4th term is double the 5th term > (ar)(ar^3) = 2(ar^4) a^2 r^4 = 2ar^4 divide by ar^4 a = 2 the sum of the first four term is 80 > a(r^4  1)/(r  1) = 80 but a = 2, so r^4  1 = 40(r  1) r^4  40r
posted on July 27, 2020 
math
We need: 4(2000 + 100q + 10r + s) = 1000s + 100r + 10q + 2 , using only whole numbers I reduced this to r = (1333 + 65q  166s)/10 made up a silly little computer program which found q = 1 r = 7 s = 8 , and of course we knew p = 2 check: is pqrs×4=srqp is
posted on July 27, 2020 
Math
common sense solution: if 7ducks eat 20 lbs of bread in 12 days ..... then twice as many ducks will eat twice as much food in the same time or twice as many ducks will eat the same amount of food in half the time Since you didn't ask a question, who is to
posted on July 27, 2020 
Math
a + s = 24 or s = 24a 25a + 15s = 490 or 5a + 3s = 98 after dividing each term by 5 use substitution 5a + 3(24a) = 98 solve for a, then you can find s
posted on July 27, 2020 
Mathematics
So he has 1/3 of his money left If he had x originally, then (1/3)x = 30 x = 90
posted on July 27, 2020 
Algebra 1
What you want : Write an expression for the statements  "In 2 years, Casey will be 3 times as old as Mary" let Mary's present age be x then in 2 years, Mary will be x+2, and Casey will be 3(x+2) So Casey's present age is 3(x+2)  2 one year from now Casey
posted on July 27, 2020 
mathematics
Had no idea what a "trapezoid Calculator" is, so I googled, which you could have done as well. "http://www.1728.org/quadtrap.htm" For the quadratic equations and all forms of great math stuff, don't you just love
posted on July 27, 2020 
Mathematics
Assuming the pyramid sits on top of the cube .... Vol = 28^3 + (1/3)(28^2)(16) cm^3 = ...
posted on July 27, 2020 
Mathematics
or prove that (n^2 − n) is divisible by 2 for all n ≥ 0 1. test if true for n = 1 11 = 0 , I guess that is true 2. assume that it is true for n = k, that is : k^2  k is divisible by 2 3. show that it must be true for n = k+1 using the fact that if
posted on July 27, 2020 
mathematics
make your sketch On mine, using the cosine law, I get x^2 = 200^2 + 150^2  2(200)(15)cos65° ..x = 192.72.. km then by the sine law, sinø/150 = sin65/192.72.. ø = 44.86..° I will let you translate that angle into your bearing notation other way....
posted on July 27, 2020 
Mathematics
first number  x 2nd number  y x + y = 5 > y = x  5 5x = 2y 5x = 2(x5) your turn, take over Hint, the answers are fractions
posted on July 26, 2020