Wednesday
August 31, 2016

Posts by Reiny

Total # Posts: 35,615

Math Algebra 2
m = m0/(sqrt (1 - (v^2/c^2)) ---> notice I fixed your mismatched brackets m(sqrt (1 - (v^2/c^2)) = m0 square both sides m^2(1 - v^2/c^2) = m0^2 expand m^2 - m^2 v^2/c^2 = mo^2 multiply each term by c^2 c^2 m^2 - m^2 v^2 = m0^2 c^2 c^2 m^2 - m0^2 c^2 = m^2 v^2 divide by m^2 ...
April 4, 2016

Math
let Sue's amount be x then Jane has x-20 and Harry has x-30 x + x-20 + x-30 = 160 solve this easy equation for x, and sub into my definitions
April 4, 2016

Math
slope between the first two points = (-3+4)/(1-0) = 1 checking for a second pair, 1st and last slope = (-1+4)/(3-0) = 1 I will let you check that the other 4 combinations yield the same slope of 1
April 4, 2016

mathematics
7(a+6d) = 11(a+10d) 7a + 42d = 11a + 110d -4a = 68d a = -17d term18 = a + 17d = -17d + 17d = 0
April 4, 2016

algebra
first piece --- x second piece --- 2x third piece --- 4x+3 solve x + 2x + 4x+3 = 38 it is easy.
April 4, 2016

Algebra
Hard to tell without the original question. As collins pointed out, your answer and the apparent correct answer do not match. State the original question and how you got your answer.
April 4, 2016

precalc
4^log16 7 = (16^(1/2))^log16 7 = (16)^((1/2))^log16 7) = 16^log16 sqrt(7) recall the property that a^loga k = k 16^log16 sqrt(7) = sqrt(7) or , using your calculator 4^log16 7 = 4^(log7/log16) = 4^.70183873 = 2.645751309 and sqrt(7) = 2.645751311 not bad
April 4, 2016

geometry
AB = sqrt(16^2 + 8^2) = 5sqrt(5) AC = sqrt(8^2 + 4^2) = 4sqrt(5) then CB = sqrt(5) C divides AB in the ratio of 4:1
April 3, 2016

maths
Just translate into Math using the definitions of AP "the fifth term is three times the second term " ---> a+4d = 3(a+d) a+4d = 3a+3d d = 2a ** "the sum of the first ten terms is 50" --> 5(2a+9d) = 50 2a+9d=10 *** sub ** into *** 2a+9(2a) = 10 20a=10 ...
April 3, 2016

algebra
Yes, I think I had that. Look at my definition of t
April 3, 2016

algebra
let the time taken by the cabin cruiser to catch up to the boat be t hours So 33t = 11(t+3) 33t = 11t + 33 22t = 33 t = 33/22 = 3/2 check: the boat went for 3+3/2 or 4.5 hours at 11 mph, went 49.5 miles the cruiser went for 3/2 hours at 33 mph, went 49.5 looks like it caught ...
April 3, 2016

math
-4x^2-4x+15 = -(4x^2 + 4x - 15) = -(2x - 3)(2x + 5) What method did you learn to solve a quadratic trinomial ?
April 3, 2016

Math
x^2 + 4x - 31 = a x^2 + 4x - 31 - a = 0 to have one root: 4^2 - 4(1)(-31-a) = 0 16 + 124 + 4a = 0 4a = -140 a = - 35 if f(x) = -35 x^2 + 4x - 31 = -35 x^2 + 4x + 4 = 0 (x+2)^2 = 0 x+2 = 0 x = -2 ----> only one root
April 3, 2016

Math
the way you typed it, the domain is the set of real numbers, x ≠ 0 What you probably meant is f(x) = (3x-7)/(x+1) In that case, the domain is the set of real numbers, x ≠ -1
April 3, 2016

Math
number of good ones --- x number of not-goods --- y cost = 7.5x + 7.5y return = 7.90x + 7.70y 7.9x + 7.7y - 7.5x - 7.5y = 34 .4x + .2y = 34 2x + y = 170 y = 170-2x There is no unique answer, unless you supply more information. I could pick any value of x between 0 and 85, and ...
April 3, 2016

Algebra
If the boat went 27 km, the raft went 17 km when they met. let the speed of the current (as well as the raft) be x km/h then the speed of the boat going upstream is 12-x km/h time taken by the raft = 17/x time taken by the boat = 27/(12-x) The difference in their times = 2 2/3...
April 3, 2016

Math
let the 3 numbers be x, y, and z from smallest to largest x+y+z = 18 z-x = 26/5 z = 26/5 + x into the first: x + y + 26/5 + x = 18 2x+y = 64/5 y = 64/5 - 2x = (64-10x)/5 but x, y, and z are to be mixed numbers, that is, they must all be greater than 1 so to find y, 64-10x >...
April 3, 2016

Math
youngest --- x oldest ---- 2x middle ---- x+3 x + 2x + x+3 = 27 solve for x
April 3, 2016

Maths - calculus
from the asymptote b/a = 18/5 , but b = 9 b/a = 9/2.5 x^2/(2.5)^2 - y^2/81 = -1
April 3, 2016

Algebra
Since both right sides are equal to y, we can say: 2x+2 = -2x-6 4x = -8 x = -2 back into y = 2x+2 y = 2(-2) + 2 = -2 x = -2, y = -2
April 2, 2016

math
careful with the notation: A statement such as 25-35 = 10 is incorrect , you have to say |25-35| = 10 that is where the "absolute" part of the definition comes in. Your arithmetic is fine.
April 2, 2016

Math
general principle of a fulcrum: If a mass of p units is placed x units from the fulcrum and it balances a mass of q units at y units on the oppose side from the fulcrum , then px = qy so make a sketch placing the 1 gram weights at the given distances The the fourth weight on ...
April 2, 2016

math
I agree
April 2, 2016

Math
Steve has answered several of these type of questions for you, here is just one of them where he showed you step by step how to do them. http://www.jiskha.com/display.cgi?id=1459622265 show us your steps you have taken for this question so we can see where your problems lie .
April 2, 2016

Math
number of nickels --- x number of dimes ----- 5x 5x + 10(5x) = 5775 solve for x, it is easy
April 2, 2016

Algebra
Oh for goodness sake! I proved to you that the answer is correct What do you mean by "I try to plug this answer in to the system " ?? What system? " it says it is incorrect" who is this "it" ??? show me the steps, perhaps I can see your error.
April 2, 2016

Algebra
You must be referring to http://www.jiskha.com/display.cgi?id=1459102205 I stand by my answer, I even proved at the end that it was correct. Have you considered that the text might be wrong?
April 2, 2016

Math
420 ft^2/f ft^2 = 36 min/30 min 420/f = 36/30 36f = 30(420) f = (30)(420)/(36) = 350
April 2, 2016

Math
3s + 9c = 75 ** 8s + 5c = 67 *** ** times 5 ---> 15s + 45c = 375 *** times 9 --> 72s + 45c = 603 subtract them: 57s = 228 s = $4.00 sub s = 4 into ** and solve for c
April 2, 2016

math
original fraction --- x/y new fractions ------- 1.6x/.8y = 2x/y it increased by 100% e.g. suppose the fraction was 5/8 new fraction = 1.6(5)/(.8(8)) = 8/6.4 = 80/64 = 10/8 ---> twice the 5/8
April 2, 2016

Math
#1 I will interpret that as: 2log (squarerootx) -log (4/3x^2) + log(4x^3)/log(100) = 2log x^(1/2) - (log4 - log3 - 2logx) + (log4 + 3logx)/2 = logx - log4 + log3 + 2logx + (1/2)log4 + (3/2)logx = (9/2)logx - (1/2)log4 = (1/2)(9logx - log4) or, = (1/2) log(x^9/4) = log [x^9/4...
April 2, 2016

math
p=log(squareroot8)/log(2) = log 8^(1/2) / log2 = (1/2)log 2^3 / log2 = (3/2) log2/log2 p = 3/2 log(31+log(16)/log(x))/log(9)=log(squareroot8/log(2) I see "mismatched brackets" on the right side. Where does p = 3/2 enter the picture?
April 2, 2016

Maths
area of whole circle = Pi(20)^2 = 400Pi Using a simple ratio: A/400Pi = 120/360 A = 400Pi/3 cm^2 = ....
April 2, 2016

math( pls help me out)
I disagree The probs that Bob found would each have 4 children, not three prob(of 3 children, two are girls) = C(3,2)(1/2)^2 (1/2) = 3/8 illustration: BBB BBG BGB GBB GGG GGB -- 2 GIRLS GBG -- 2 GIRLS BGG -- 2 GIRLS So there are 3 cases of 2 girls prob(2 girls) = 3/8 prob(3 ...
April 2, 2016

another approach - math
Ok, how about this approach sinA = x + cosA x = sinA - cosA let's change sinA - cosA into a single sinusoidal expression: Let sinA - cosA = a sin(A + k) a sin(A+k) = a(sinAcosk + cosAsink_ = asinAcosk + acosAsink then asinAcosk = sinA acosk = 1 cosk = 1/a acosAsink = -cosA...
April 2, 2016

math
I did this yesterday http://www.jiskha.com/display.cgi?id=1459511832
April 2, 2016

Maths
A 45 degree sector is 1/8 of the circle So find (1/8)(pi)(14^2)
April 2, 2016

math
prob(get money) = .3 prob(not get money) = .7 prob(at least 3 of 5 get money) = C(5,3)(.3)^3 (.7)^2 + C(5,4)(.3)^4 (.7) + .3^5 = .. you do the button-pushing
April 2, 2016

Math
by simple observation, the x's increase by 2 , so 20+p = 21 thus p=1 which lets the y's increase nicely by 1
April 2, 2016

math
prob(buy) = .4 prob(not buy) = .6 prob(5 of 10 will buy) = C(10,5) (.4)^5 (.6)^5 = 252(.000796..) = appr .2007
April 2, 2016

Algebra
in the first, replace x with -3 and solve for y in the second, replace y with 1 and solve for x
April 1, 2016

Math
distance from (3,4) to (-1,0) = sqrt(4^2 + 4^2) = sqrt(32) = appr 5.7 where you just guessing?
April 1, 2016

Math- quadratic equation
width of pathway = x m width of whole thing = 12+2x m length of whole thing = 16+2x (12+2x)(16+2x) = 258 192 + 56x + 4x^2 = 258 2x^2 + 28x - 33 = 0 x = (-28 +- sqrt(1048))/4 = 1.093 or a negative the path should be appr 1.09 m wide all around check: (12+ 2.18)(16+2.18) = 14.18...
April 1, 2016

Math
looks like for every increase of 1 in the x, our y decreases by 5 so it must be y = -5x + c all we need is to find c pick one of the data values: 0 = 0, y = -1 -1 = 0 + c c = -1 y = -5x - 1
April 1, 2016

trigonomentry out of ideal help ah!crying
cute problem recall that cos x = - cos(180 - x) that is cos(1) = - cos(179) cos(3) = - cos(177) .. cos(89) = - cos(91) cos(91) = - cos(89) ... cos(177) = - cos(3) cos(179) = - cos(1) so : cos1 + cos3 + ... + cos 177 + cos 179 = (cos1+cos179) + (cos3+cos177) + ...+ (cos89+cos91...
April 1, 2016

typo - Math
I did this on paper first, but then messed up when I typed it. the first few lines in the equations should have been: (x+1)(x - (1+i))(x - (1-i)) = 0 (x+1)(x-1-i)(x-1+i) = 0 (x+1)(x^2 - x + xi -x +1 -i -xi + i - i^2) = 0 the rest is fine
April 1, 2016

Math
complex roots always come in conjugate pairs, so if one is 1+i, you must have another as 1-i so we know the equation is (x+1)(x - (1+i))(x + 1+i) = 0 (x+1)(x-1-i)(x+1+i) = 0 (x+1)(x^2 + x + xi -x -x -i -xi - i - x^2) = 0 (x+1)(x^2 - 2x + 2) = 0 x^3 - x^2 + 2x + x^2 - 2x + 2 = ...
April 1, 2016

Mathematics
trying your choice: for (2,-1) in y = 2x - 1 -1 = 2(2) - 1 -1 = 3 ???? not every likely. try the others the same way.
April 1, 2016

Math
Since the sine is negative and the tangent is positive, the angle is in quadrant III from sin theta = -4/9, r = 9 and y = -4 x^2 + y^2 = r^2 x^2 + 16 = 81 x = -sqrt(65) , in III the x is negativ Then cos theta = -sqrt(65)/9 sec theta = -9/sqrt(65) or -9sqrt(65)/65
April 1, 2016

math
let sinA = x + cosA x = sinA - cosA x^2 = sin^2 A - 2sinAcosA + cos^2 A x^2 = 1 - 2sinAcosA x^2 = 1 - sin 2A x = +/- sqrt(1-sin(2A)), |sin 2A| <= 1 not sure if that is what you want. Since I squared the equation, any (A,x) would have to be verified
April 1, 2016

math
Since no letters repeat, this is straightforward. number of "words" = 9! = 362880
April 1, 2016

Math
4 queens or 4 fives prob(of stated event) = 8/52 = 2/13
April 1, 2016

Math
In any of these kind of problems , n has to be a whole number, that is n = 1,2,3, .... My choice would be term(n) = 5n - 1 , which is the only one that makes term(1) = 5(1) - 1 = 4 your choice would produce a first term of 9, which is the second term, not the first your ...
March 31, 2016

Algebra 2
interpretation: the division must be excact, that is, there cannot be a remainder. Arrange the terms in the proper order and do a synthetic division: -1 | -2 1 -1 1 ....... 2..-3..4 .... -2 3..-4..5 so we should have had a 0 instead of a 5 at the end of our algorithm, that ...
March 31, 2016

Math
A is the only one that works our pattern.
March 31, 2016

Math
#1 notice that the terms keep getting smaller, so we clearly are adding a -6 What number did we start with? #2 the correct choice would be -64, -128, -256 which I don't see, unless you have a typo
March 31, 2016

Pre cal 11
let 5b-3 = x, then we have 4x^2 + 10x - 6 = 2(2x^2 + 5x - 3) = 2(x+3)(2x-1) replace x with 5b-3 within each bracket , then simplify
March 31, 2016

Calculus
If your function contains terms of the type ax^2, ay^2, ax, and ay along with some constant terms , and where a is a rational number, then you have a conic if it contains terms such as xy , it could be a conic that has been rotated, and is no longer parallel or perpendicular ...
March 31, 2016

Maths
What the question does not say, but what I will assume is true to have your answer of 10, is that the dimensions must be whole numbers. Otherwise there would be an infinite number of cases So we need 3 multipliers (LWH) to get 28 the factors of 28 in triples are 1 1 28 1 2 14 ...
March 31, 2016

math
For the 10 K race in 58 minutes the runner would take 5.8 minutes per km or 5 minutes and 48 seconds to run 1 km The equivalent race of 6.2 miles would have a time of 58/6.2 minutes per mile or 9.3548.. minutes per mile = 9 minutes, 21 seconds (A real runner doing a 10 K race ...
March 31, 2016

math
the average of 200 and 160 is 180 so the speed of the plane with no wind is 180 mph, and the wind speed is 20 mph check: going against the wind = 180-20 = 160 going with the wind = 180 + 20 = 200
March 31, 2016

@ AMANSANDHUWILLDIE - pr calc 11
You might have noticed that Steve did not reply to your question. You may talk in a disrespectful way to your peers the way you did, but calling a distinguished professor "dude" is not the smartest thing to do. I am sure one of your fellow dudes might suggest that ...
March 31, 2016

Math
hearts OR ten = 13 + 4 - 1 = 16 (can't count the 10 of hearts twice) continue
March 31, 2016

Geometry
Oh my goodness! What has happened to each of the coordiates of the two points? Why was 6 your choice? How can you "feel" an answer to be right?
March 31, 2016

Math
I was able to see your diagram. Since the band circle must have a total of 25, and we have already (11+7+3) or 21 entered in the Venn diagram, the missing part of Band and Choir must be 4 So label the math-only part 9 and the intersection of Math and Choir as x (only the part ...
March 31, 2016

Math
Look at the previous post and simply change the numbers
March 31, 2016

Math
The number of ways to select 7 from 1 to 45 = C(45,7) = 45,379,620
March 31, 2016

math
The HCF of 64 and 124 is 4 The LCM of 64 and 124 is 1984 so what is 1984/4 ?
March 31, 2016

business math
100(r)(2/52) = 2.50 r = (2.5/100)(52/2) = .65 = 65% The equivalent annual rate is 65% (In the middle ages they would have been burned at the stake for usury.)
March 31, 2016

Math
wins --- x ties --- y x+y= 18 2x+y= 30 subtract them: x = 12 then y = 6 wins: 12 losses: 10 ties: 6 check: 2(12) + 0(10) + 1(6) = 30
March 31, 2016

Trig
make sketches of two right angles triangles in the third quadrants since tanA = 3/4, the terminal arm of angle A ends at (-4,-3) , and r = 5 so sinA = -3/5, and cosA = -4/5 (you have a 3-4-5 right-angled triangle) since cosB = -5/13 , the terminal arm of angle B ends at (-5,-...
March 31, 2016

Math
term(n) = -3n + 27
March 31, 2016

math
.05(3000) + .08x = .075(3000+x) 150 + .08x = 225 + .075x .005x = 75 x = 15,000 check: total invested = 3000+15000 = 18000 .075(18000) = 1350 interest at partial investments = .05(3000) + .08(15000) = 150 + 1200 = 1350 How did you possible get $279,375 ??? Did that sound ...
March 31, 2016

Algebra
x + (1/7)x = 88 hint: multiply each term by 7 to clean up the fraction, and solve for x
March 31, 2016

Algebra 1-Factoring Help!
Somebody had the same question earlier today. http://www.jiskha.com/display.cgi?id=1459354736
March 30, 2016

math
correct, 10% of 80 is 8 so prob of fail = 8/80 = 1/10 so for 400 units, prob = (1/10(400) =
March 30, 2016

math
what is 10% of 80 ?
March 30, 2016

Math
looks like a simple typo here actually 4/52 = .0769... = .08 correct to 2 decimals
March 30, 2016

NO - Math
no The order in which the cards are drawn should not matter. They even used the word "combination", which implies that the order does not matter. So you are simply choosing 2 of the 9 cards = C(9,2) = 9!/(2!7!) = 36 The answer of 72 would be correct if the order in ...
March 30, 2016

Math
cylinder1: height = h radius = r volume = pi r^2 h = pi r^2h cylinder2: height = h radius = 2r volume = pi (2r)^2 h = 4pi r^2h or ratio is 1 : 4 so the volume is 4 times as large
March 30, 2016

Trigonometry
correct conclusion
March 30, 2016

Trigonometry
Your probably made a sketch and have learned the sine law If not, go to the construction part of my reply using the sine law: sinA/30 = sin54/20 sinA = 1.2135.... but that is not possible , since the sine of any angle has to be between -1 and 1 So there is no such triangle ...
March 30, 2016

math (ms sue)
Note that your 3 probabilities do not add up to 1, thus other parties must also have received votes Your want the prob(CP OR L) = .36+.23 = .59
March 30, 2016

algebra
frame = (3+2x) by (5+2x) (3+2x)(5+2x)= 35 15 + 16x + 4x^2 = 35 4x^2 + 16x - 20 = 0 x^2 + 4x - 5 = 0 (x-1)(x+5) = 0 x = 1 or x = -5 , the last one is not possible the frame is 5 cm by 7 cm
March 30, 2016

Algebra 1-HELP!
small typo should have said: step2: look for 2 factors which multiply to get -18, and whose sum is the middle term coefficient But you probably figured that out anyway.
March 30, 2016

Algebra 1-HELP!
first arrange them in the standard order 18x^2 + 21x - 9 look for a common factor, in this case 3 18x^2 + 21x - 9 = 3(6x^2 + 7x - 3) A method which seems to be popular these days is "decomposition", (not my personal favourite) Step1: multiply the (a)(c) (6)(-3) = -18...
March 30, 2016

mathd
Make a sketch, label the top of the building P and its bottom Q. On the ground, label angle A = 20 and mark point B as 23 degrees then angle ABP = 180-23 = 157 degrees angle A = 20 and angle APB = 3 degrees by the sine law BP/sin20 = 80/sin3 BP = 80sin20/sin3 = .... then in ...
March 29, 2016

Math
number of club members --- x girls ---- 3x/8 number of 6th grader girls = (2/5)(3x/8) = 3x/20 fraction of 6th grade girls = (3x/20) / x = 3/20
March 29, 2016

algebra
You used the word "combination" which implies that the order does not matter. We will also assume that flavours cannot be repeated, e.g. no double-vanilla Number of combinations = C(38,3) = 38!/(3!35!) = 8436
March 29, 2016

math
All I did is to translate the English into Math Let Sandy's age be x "Jay is as twice as old as Sandy " ----> Jay's age is 2x "Jay is 2 years younger than Mike" ---> Mike's age is 2x+2 "Mike is 7 years older than Sandy" ---> ...
March 29, 2016

math
Sandy --- x Jay------- 2x mike ----- 2x+2 "Mike is 7 years older than Sandy " ---> 2x+2 = x+7 x=5 check: Sandy is 5 Jay = 10 Mike is 12 Is Mike 7 years older than Sandy? YES
March 29, 2016

Algebra
since both say y = we equate: x^2+2x=3x+20 x^2 - x - 20 = 0 (x-5)(x+4)=0 x=5 or x=-4 for x=5, y = 35 for x=-4, y = 8
March 29, 2016

math
ramus age --- 3x sister's age --- 4x but 4x = 36 x = ... carry on.
March 29, 2016

math
The number of ways to select 7 from 1 to 45 = C(45,7) = 45,379,620
March 28, 2016

math
any 3 positive numbers which have a product of 64 There would be an infinite number of ways, one of them is 4 cm by 8 cm by 2 cm , another is 2.25 by 7 by 256/35
March 28, 2016

Math
you already know the equation must be y = a(x+2)^2 - 3 All that is missing is the value of a To find a, plug in the given point and solve for a. Rewrite my equation and you are all done.
March 28, 2016

math
Wow! - slop is something they feed to pigs. - you have the same point listed twice - "undefied" ??? , probably meant undefined.
March 28, 2016

Math
no, you cant add them notice you would have a probability equal to 1, which means the event you want will always happen. prob(yellow, black, then white) = (5/10)(3/9)(2/8) = 1/24 notice that each time a sock is pulled there is one less to choose from, hence the decreasing ...
March 28, 2016

Math
part 1 No idea, since you didn't tell us what he paid for them part 2 So he had 35% of the 500 oranges left or 175 of those 8% went bad so he still had 92% of the 175 to sell or 161 return per orange = 24.15/161 = .15 he sold them at 15 cents each ( good price, must be an ...
March 28, 2016

Algebra
(5√2 − √5)(5√2 − 5√5) = 50 - 25√10 - 5√10 + 25 collect your like terms and simplify
March 28, 2016

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