Friday
August 22, 2014

Posts by Reiny


Total # Posts: 26,966

Math
Did you make a diagram? Did you not realize that the direction of the plane and the wind form a right angle ? How did you get 266.4 for the groundspeed ? (I got 241.86)
March 16, 2014

Math 2 questions
volume of 2 similar solids is proportional to the cube of their corresponding sides, so x/240 = 23^3/92^3 = (23/92)^3 = (1/4)^3 = 1/64 64x = 240 x = 3.75 the new volume is 3.75 ft^3 If I told you that the surface area of 2 similar solids is proportional to the square of their ...
March 16, 2014

Math
number of chairs --- x number of tables --- 14-x 30x + 70(14-x) = 660 solve for x, pretty straightforward.
March 16, 2014

can u explain? 1 question
volume of pyramid = (1/3) area of base x height
March 15, 2014

i need yur help with this..
look at my answer to your first question here http://www.jiskha.com/display.cgi?id=1394926846 In calculating the area of the triangle, the height is not 15. make a sketch of the triangle to see that 15 is the hypotenuse.
March 15, 2014

Calc
quick way: for a given point (p,q) , the shortest distance from that point to the line Ax + By + C = 0 is |Ap + Bq + C|/)√(A^2+B^2) so we have (p,q) = (-4,-4) and line 2x - 2y + 3 = 0 distance =|-8 +8 + 3|/(4+4) = 3/√8 = 3/√8*√8/√8 = 3√8/8...
March 15, 2014

math
could be a very nasty equation but .... 3^x + 4^x = 5^x by inspection and recall, I know that 3^2 + 4^2 = 5^2 (did you recognize the 3-4-5 right-angled triangle) so x = 2 now suppose it had been 3^x + 4^x = 6^x look at Wolfram's solution http://www.wolframalpha.com/input/?...
March 15, 2014

Math help plz check my answers!
Surface area of a square pyramid usually just adds up the surface area of the 4 isosceles triangles, not including the base one of them: base = 11 hypotenuse = 15 height^2 + 5.5^2 = 15^2 height^2 = 194.75 height = √194.75 area of one of them = (1/2)(11)√194.75 = ...
March 15, 2014

Algebra II
I am sure you meant: (4-7i)/(2+5i) = (4-7i)/(2+5i)*(2-5i)/(2-5i) = (8 -20i - 14i + 35i^2 )/(4 - 5) = 8 - 34i - 35)/-1 = 27 + 34i
March 15, 2014

Pre-Calculus
5 - 12i r = 13 , but we want it in the form r(cosØ + isinØ) cosØ = 5/13 , so Ø could be in I or IV sinØ = -12/13, so Ø could be in III or IV so Ø must be in IV taking Damon's angle of 292.6° 5 - 12i = 13(cos292.6 + i ...
March 15, 2014

Algebra Question~!
x^2 + 7x - 30 = (x+10)(x-3) so the sides could be (x+10) and (x-3) , were x > 3 or x^2 + 7x - 30 = (x-2)(x+9 - 12/(x-2) ) so the sides could be x-2 and x+9 - 12/(x-2) or x^2 + 7x - 30 = (x+5)((x+2 - 40/(x+5) ) so the sides could be x+5 and x+2 - 40/(x+5) or ... as you can ...
March 15, 2014

Algebra Question~!
you should know the formula for the area of a circle just plug in 3x+2 for r and look at your choices (which you did not give us)
March 15, 2014

math
did that one for you, look for your previous post
March 15, 2014

mathematics
tough one! are you sure you did not mean 4^x = 8^x ? that would be easy. What you typed requires some sort of sophisticated method such as "Newton's Method" but an intuitively obvious answer would be x = 2 however there is another one between 0 and 1 let me know ...
March 15, 2014

math
looks like a lot of nonsense and mathematical gibberish.
March 15, 2014

geometry
make a sketch, join the centre to A, and complete the right-angled triangle. let the distance from the centre to the chord be x x^2 + 5^2 = 13^2 x^2 = 169-25 = 144 x = √144 = 12 Where does CD enter the picture? Where is D ? Your opening sentence of "center C has a ...
March 15, 2014

math
all lines of the type y = (-3/2)x + b , where b is any real number would be perpendicular to your given line Where there any choices? so just make sure the answer starts with y = (-3/2)x ...
March 15, 2014

Algebra Question~!
area of lot = (6x)(9x) = 54x^2 area of circle = π(4x)^2 = 16πx^2 amount left over = 54x^2 - 16πx^2 = (54-16π)x^2
March 15, 2014

math
let the original cost of one shirt be x so three shirts cost 3x reduced by 30% leaves you with .7(3x) .7(3x) = 63 2.1x = 63 x = 63/2.1 = 30 Just noticed this same question was asked last year. http://www.jiskha.com/display.cgi?id=1361331485 Now you have 3 different solutions, ...
March 15, 2014

math
What is 8/9 - 3/5 ?
March 15, 2014

geometry
As I understand the question, you simply want the circumference of a sector of central angle 7(15°) or 105° with a radius of 24 cm circumference of a circle with radius 24 is 48π cm so using a simple ratio ... 105/360 = x/48π gives an arc length of 105(48&#...
March 15, 2014

Finance
You have conflicting information. At the beginning of his "retirement period" he will need: 35000( 1 - 1.08^-15)/.08 = 299,581.75 so he would not need $400,000 at that time. To assure that he will have that $299,581.75 available 20 years from now , he needs a present...
March 15, 2014

Trigonometry
using sin(A+B) = sinAcosB + cosAsinB 4sin(π/2+x) = 4(sin(π/2)cosx + cos(π/2)sinx) = 4( (1)cosx + (0)sinx) = 4 cosx
March 14, 2014

Probability
I too made a Venn diagram and after filling in the given information , found two missing sections 1. Those that only walked 2. Those that took the bus or the car, but did not walk confirm this please #2, dA/dr means the rate of change of the surface area with respect to the ...
March 14, 2014

math
I = PRT 960 =4000(R)(3) solve for R (I got 8%)
March 14, 2014

Calculus
Steve is right, I made a silly adding vs subtracting error in the 3rd last line 3y + 27/5 = 2x - 48/5 3y - 2x = -21/5 should be 3y + 27/5 = 2x - 48/5 3y - 2x = -75/5 to give 10x - 15y = 75 , reducing to 2x - 3y = 15
March 14, 2014

Calculus
the the point of contact be P(x,y) Make a sketch to see that there would be two points P 2x + 8y dy/dx = 0 dy/dx = -2x/(8y) = -x/(4y) slope of tangent = (y-3)/(x-12) then (y-3)/(x-12) = -x/(4y) 4y^2 - 12y = -x^2 + 12x x^2 + 4y^2 = 12x + 12y but x^2 + 4y^2 = 36 12x + 12y = 36 x...
March 14, 2014

Happy Pi Day
OOPS, good catch, my apologies to the good people of Illinois.
March 14, 2014

Happy Pi Day
From the article: "The Illinois Science Council and Fleet Feet Sports are hosting a 3.14-mile walk/run Friday night, ." It is ironic that the state of Illinois actually introduced a bill , the notorious #246, which attempted to declare the value of π to be 3. ...
March 14, 2014

math
from the given: term(3) = ar^2 = 28 term(4) = ar^3 = -56 so ar^3/(ar^2) = -56/28 r = -2 then in ar^2 = 28 a(4) = 28 a = 7 sum(6) = a(r^6 - 1)/(r-1) = 7((-2)^6 - 1)/(-2-1) = 7(63/-3) = -147 check: GP is 7, -14 , 28 , - 56 , 112, - 224 sum of that is -147
March 14, 2014

math
You state different interest rates for the 1st and 3rd debt, but state no rate for the 2nd debt of $2000 due in 2 years. Other than , choose a time as a reference or focal date I picked the present time, so at present, the value of the debt = value of payments 500(1.03)^-2 + ...
March 14, 2014

Math
cost of 1st machine = 250000 + 30000( 1 - 1.085^-10)/.085 - 75000(1.085)^-10 = 413,669.04 cost of 2nd machine = 400000 + 225000(1.085)^-5 - 175000(1.085)^-10 = 472,235.27 1st is cheaper, I used the present time as my "focal point in time" check my arithmetic
March 14, 2014

Algebra 1
so we want a^2 = b^3 a = b^(3/2) or (√b)^3 so pick b = a perfect square, e.g. b = 4 , then a = 8 so 8^2 = 4^3 = 64 let b = 9 , a = 27 9^3 = 27^2 = 729 let b = 16 , then a = 64 16^3 = 64^2 = 4096 let b = 25 , a = 125 25^3 = 125^2 = 15625 So the first few numbers with that...
March 8, 2014

Albegra
I would first of all divide both sides by 20 to get the numbers a bit smaller 121/(570+r) = 107(570-r) now cross-multiply 60990 + 107r = 68970 - 121r 228r = 7980 r = 7980/228 = 35 or, look at it this way: the LCD is (570+r)(570-r) so in effect I just multiplied both sides of ...
March 8, 2014

applied algebra
what is 800(1.0275)^14 ?
March 8, 2014

math
3x^2 - 24x + 45 =0 first divide by 3 to simply x^2 - 8x + 15 = 0 (x-3)(x-5) = 0 x = 3 or x = 5 check: http://www.wolframalpha.com/input/?i=plot+y+%3D+3x%5E2+-+24x+%2B+45
March 8, 2014

math
To have more than 30 cents, the right pocket must have the quarter and the dime. possible cases, order does not matter: L --- left pocket, R -- right pocket L -- R QP ND QN PD QD PN PN QD PD QN ND QP -----> so we have 6 cases prob = 1/6
March 8, 2014

Math
y = 2(x^2 - 2x +1 -1) - 6 = 2( (x-1)^2 - 1) - 6 = 2(x-1)^2 - 2 - 8 = 2(x-1)^2 - 10 the vertex is ........
March 8, 2014

Math
y=x^2 - 4x-21 = (x^2 - 4x + 4 - 4) - 21 = ( (x-2)^2 - 4) - 21 = (x-2)^2 - 4 - 21 = (x-2)^2 - 25 take over
March 8, 2014

MATH
I agree with Damon that your gravitational constant is off. Since you are using metric , your equation should be h = -4.905t^2 + 16t + 9 let's ballpark it to h = -5t^2 + 16 + 9 a) ..... b) sub in t = 1 , h = -5+16+9 = 20 m c) for t of the vertex ... t =-b/(2a) = -16/-10 = ...
March 8, 2014

Statistics
I thought I had given you the answer. finding the z-score results in a mean of 0 and a standard deviation of 1 so in the link I gave you .... http://davidmlane.com/hyperstat/z_table.html enter 0 for the mean 1 for the sd click on "below" and enter -.75 click on "...
March 8, 2014

further maths
calculate the area of a circle with 23 m - area of circle with 20 m. = (23^2)π - (20^2)π = .....
March 8, 2014

Statistics
Fun to play around with this excellent site http://davidmlane.com/hyperstat/z_table.html
March 8, 2014

Statitics
prob(lost) = 5/1000 = 1/200 prob(not lost) = 199/200 prob( 2 of 22 are lost) = C(22,2) (1/200)^2 (199/200)^20 = .005224.. Question for you. would this be the same as "....a group of people who have 11 pieces of luggage. What is the probability that 1 of these are lost? &...
March 8, 2014

Statistics
Use David's excellent "normal distribution" calculator http://davidmlane.com/hyperstat/z_table.html click on "area from a value" enter the data, click on "between" and enter 8 and 11 to get .4467 You can enter the data directly, no need to ...
March 8, 2014

maths
There are 2 ways to get a sum of 11 in a throw of 2 dice --- 6,5 or 5,6 prob of sum of 11 = 2/36 = 1/18
March 7, 2014

Algebra
Hint for the factors: Can you think of 2 numbers, one positive and the other negative, which when multiplied give you -30 and when added give you +7 ?
March 7, 2014

Algebra 1 Answer Check (Reiny)
you are welcome
March 7, 2014

Algebra 1 Answer Check (Reiny)
all 3 are correct.
March 7, 2014

Calc :(((((
first cross-multiply y + y x^2 = x dy/dx + y(2x) + 2x dy/dx = 1 dy/dx(1 + 2x) = 1 - 2xy dy/dx = (1-2xy)/(1+2x) at (4, 1/4) dy/dx = (1 - 2(4)(1/4))/(1 + 2(4)) = -1/9 equation of tangent: y = (-1/9)x + b at (4,1/4) 1/4 = (-1/9)(4) + b b = 5/9 equation is y = (-1/9)x + 5/9 slope...
March 7, 2014

Calculus Help
dy/dx = 2ax + bx when x = 1, 2a + b = 6 when x = -1 -2a +b = -14 add them 2b = -8 b= -4, then a = 5 to find c, sub in (2,17) into the original: 17 = 4a + 2b + c 17 = 20 -8 + c c = 5 y = 5x^2 - 4x + 5 check: for (2,17) 17 = 20 - 8 + 5 ---> true dy/dx = 10x - 4 at x = 1, dy/...
March 7, 2014

Algebra word problem
x^2 + 6x - 27 = (x+9)(x-3) So possible sides are x+9 and x-3 however, that would not be the only possibility. e.g. suppose one side is x-2 then the other side is (x^2 + 6x - 27)/(x-2) or ( x+8 - 11/(x-2) ) or with actual values suppose the area is 27 and one side is 3 then we ...
March 7, 2014

Probability
let N be a normal coin, and let DH be a double - headed coin let DT be double-tailed H -- heads, T --- tails for N, prob(H) = 1/2, prob(T) = 1/2 for DH, prob(H down) = 1, prob(Tdown) = 0 for DT, prob(H down) = 0, prob(Tdown) = 1 so you could draw N or DH or DT prob(heads down...
March 7, 2014

Algebra
area of lot = (6x)(10x) = 60x^2 area of field = x(4x) = 4x^2 area left for bleachers = 60x^2 - 4x^2 = 56x^2
March 7, 2014

maths
we know tht sin (-Ø) = -sinØ so if sinA = 3/5 sin(-A) = -3/5 check: from the given, A = 143.13.. sin(-143.13..) = -.6
March 7, 2014

Trig
In my sketch I see a non-rightangled triangle with angles 42° , 110° and 28° with the side opposite the 42° as the guy wire by the sine law: x/sin42 = 25/sin28 x = 25sin42/sin28 = .....
March 7, 2014

Calculus Please help!
f(-3) = 54 + 18 + 9 + 2 = 83 f(-1) = -2 + 2 + 3 + 2 = 5 slope = (5-83)/(-1+3) = -39 f ' (x) = -6x^2 + 4x - 3 then -6x^2 + 4x - 3 = -39 6x^2 - 4x -36 = 0 3x^2 - 2x - 18 = 0 x = (2 ± √220)/6 = appr 2.8054 or appr -2.1388
March 7, 2014

Calculus...URGENT..show steps please
The "solving" becomes a bit easier if you change the original equation to (x-y)^2 - 6x + 2y + 17 = 0 sub in : y = x - 3 (x - (x-3))^2 - 6x + 2(x-3) + 17 = 0 9 - 6x + 2x - 6 + 17 = 0 -4x = -20 x = 5 then y = 2 the horizontal asymptote touches at (5,2) I will do the ...
March 7, 2014

math
change in volume of tank = (5000)(4400)(21) cm^3 = 462,000,000 cm^3 = 462,000 L 15 km/hr = 1,500,000 cm/hr Volume moved = 1,500,000(49π) cm^3/hr time to fill 462,000,000 = 462,000,000/1,500,000 hrs = 308 hrs check my arithmetic
March 7, 2014

Algebra Question
Of course not! expand each of your factored expression. Notice that the middle terms are not the same
March 7, 2014

Math
part left = 1 - 3/8 - 1/3 = 24/24 - 9/24 - 8/24 = 7/24
March 7, 2014

Trig
absurd angles, check your typing. did you mean 70° instead of 700 ?
March 6, 2014

Math(check answer)
odds and probability are not quite the same odds in favour of some event = prob of that event : prob of NOT that event so ... prob of picking a green = 9/20 prob of not picking green = 11/20 odds in favour of picking a green = 9/20 : 11/20 = 9 : 11 which is D
March 5, 2014

MATH
radius after 24 hrs = 500(24) = 12000 m or 12 km area after 24 hrs = π(12)^2 = 144π square km radius after 48 hrs = 500(48) = 24000 m - 24 km area after 48 hrs = π(24^2) = 576 km^2 growth of spill between 24 hrs and 48 hrs = 432 km^2
March 5, 2014

Math
What is C(16,3) ?
March 5, 2014

Math
distance covered by faster driver --- x km distance covered by slower driver --- 320-x km The must have driven the same abount of time, so x/95 = (320 - x)/65 65x = 30400 - 95x 160x = 30400 x = 190 time = 190/95 = 2 hrs check: time of faster driver = 190/95 = 2 time of slower ...
March 5, 2014

Math
same old
March 5, 2014

Math
Are you reading my other replies to your questions with the same concept?
March 5, 2014

Math
A prime has no factors other than 1 and itself 5x^2 + x - 2 does not factor, so ....
March 5, 2014

Math
Using distance = rate x time 105t = 45(t+4) 105t = 45t + 180 60t = 180 t = 3 distance covered by each = 105(3) = 45(7) = 315 miles
March 5, 2014

Math
Very similar to the other I just answered for you. Difference in this one: the item is not replaced Prob = (6/20)(2/19) = 12/380 = 3/95
March 5, 2014

Math
oops , you wanted 3 decimals, 5.791 or 1.209
March 5, 2014

Math
use the formula x = (7 ± √21)/2 ---- > this is exact or appr, 5.79 or appr 1.21
March 5, 2014

Algebra
look at it as 2 ordered pairs (1/2 , 480) and (3/4 , 720) and find the linear equation slope = (720-480)/(3/4 - 1/2) = 240/(1/4) = 960 S = 960g + b , (using y = mx + b ) for (1/2, 480) 480 = 960(1/2) + b 480 = 480 + b b = 0 S = 960G (tells me 1 gallon covers 960 square feet)
March 5, 2014

Math
P(red, then blue) = (9/41(10/41) = 90/1681
March 5, 2014

Math
starting number --- x Anita's method 2x + x = 3x Amit: (x+x)(2) = 4x 4x - 3x = 9 x = 9 My algebra becomes the explanation. check: Anita ---> 2(9) + 9 = 27 Amit ---> (9+9)(2) = 36 difference = 36-27 = 9 all is good!
March 5, 2014

Correction - Math(Check answer)
Both are wrong Odds and probability are not the same thing you have found the prob(picking a vowel) Odds in favour of picking a vowel = prob of picking a vowel : prob of NOT picking a vowel = 3/7 : 4/7 = 3 : 4 the second question simply reverses the odds should be 4 : 3
March 5, 2014

Algebra
variance is defined as the square root of the standard deviation since variance is 4, sd = 16 go to http://davidmlane.com/hyperstat/z_table.html enter , 195 for the mean and 16 for sd click on below, and enter 190.2 to get .3821
March 5, 2014

Alg help
I had that too, hit the 4 instead of the 2, sorry.
March 5, 2014

Alg help
What is √(12^2 + 4^2 + 9^2) ?? I get √441 , which is not any of your choices.
March 5, 2014

math
what about it ?
March 4, 2014

algebra
amount invested at 5% --- x amount invested at 8% --- y x+y = 5000 (5/100)x + (8/100)y = 331 times 100 5x + 8y = 33100 first equation times 5 5x + 5y = 25000 subtract them: 3y = 8100 y = 2700 take over....
March 4, 2014

algebra
x+y = 30 x-y = 2 add them 2x = 32 x = 16 then, mentally, y = 14 check: 16+14 = 30 16-14 = 2 , yeahhh!
March 4, 2014

Differential Equations
".. by making many small deposits throughout the year. " I don't know what you mean by that. - how often are they made ? - are the payments the same ?
March 4, 2014

Algebra
volume = length x width x height = (2x+3)(x+2)(x-3) or, if it needs to be expanded .... = (2x+3)(x^2 - x - 6) = 2x^3 - 2x^2 - 12x + 3x^2 -3x - 18 = 2x^3 + x^2 - 15x -18
March 4, 2014

Math
600 g + 1 kg = 600 g + 1000 g = 1600 g = 1.6 kg
March 4, 2014

algebra (solve for y)
treat it like a quadratic equation ... let e^y = x then your equation becomes 0 = 2x^2 - x x(2x - 1) = 0 x = 0 or x = 1/2 then e^y = 0 -----> no solution or e^y = 1/2 take ln of both sides and use the rules of logs y lne = ln1 - ln2 y (1) = 0 - ln 2 y = -ln2 or e^y( 2e^y - ...
March 4, 2014

math
I will define x in a different way, the way you suggest introduces unnecessary complicated fractions. The the radius of the circle be r, let each side of the square be x 4x + 2πr = 24 2x + πr = 12 x = 6 - (π/2)r let A be the total area A = πr^2 + (6 - (&#...
March 4, 2014

math
y = cosx tanx = cosx (sinx/cosx) y = sinx
March 4, 2014

Geometry
no, it is b SSA often results in 2 different triangles with the same properties, thus no congruency.
March 4, 2014

math
square: a quadrilateral with 4 equal sides, all angles 90° rhombus: a quadrilateral with 4 equal sides. A square is a rhombus, but a rhombus is not necessarily a square. http://www.mathsisfun.com/quadrilaterals.html
March 4, 2014

Algebra - Domain
I see a few problems here. 1. In the usual terminology, the word "function" implies the relationship between two variables, usually x and y, where the value of y depends on x. You have an equation that contains only one variable y (the "solution" to your ...
March 4, 2014

Algebra
correct
March 4, 2014

math
By sheer coincidence this same question was posted on March3 , three years ago http://www.jiskha.com/display.cgi?id=1299163469
March 3, 2014

Algebra
ascending powers of b ----> the terms containing b with exponents from smallest to largest, so -7dm + 25 b^5 - 6 d b^6 + 3 b^10 your answer makes no sense, there were 4 terms, so you still have to have 4 terms.
March 2, 2014

Algebra
descending means from highest to lowest. just look at the exponents of p
March 2, 2014

Math
speed = distance /time speed ≥ 420/8 ≥ 52.5 mph
March 2, 2014

Geometry
Did you not read our objection to your problem. Why would you repost exactly the same way ? http://www.jiskha.com/display.cgi?id=1393701722 Steve gave you a solution according to one interpretation.
March 2, 2014

geometric progresions
sum of first 8 terms = a(r^8 - 1)/(r-1) sum of first 4 terms = a(r^4 - 1)/(r-1 ( a(r^8 - 1)/(r-1) ) / ( a(r^4 - 1)/(r-1) ) = 97/81 (r^8 - 1) / (r^4 - 1) = 97 / 81 81r^8 - 81 = 97r^4 - 97 81^8 - 97r^4 + 16 = 0 let r^4 = x 81x^2 - 97x+16 = 0 x = (97 ± √4225)/162 = (...
March 2, 2014

algebra
Will there be some kind of question ?
March 1, 2014

Pages: <<Prev | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | Next>>

Search
Members