Thursday
October 23, 2014

Posts by Reiny


Total # Posts: 27,528

Math
correct
October 16, 2014

math
There were 23 marbles, of which 5 were blue 3 were removed, one of them blue so now there are 20 marbles, of which 4 are blue prob(blue) = 4/20 = 1/5 which is C
October 16, 2014

algebra
width --- x length -- 3x+5 area = x(3x+5) or 3x^2 + 5x
October 16, 2014

Math
yes
October 16, 2014

Math algebra Help please
original: base --- b, height --- h area = (1/2)bh = 24 bh = 48 new triangle: base ---6b, height ----6h new area = (1/2)(6b)(6h) = 18 bh = 864
October 16, 2014

Algebra
Let the time for the first train be t hrs 50t + 70(t-1) = 350 120t = 420 t = 420/120 = 7/2 or 3.5 hrs
October 16, 2014

Math
break down of A = [ w | w < 1} A = ------ A is equal to | w ----- the set of all w such that w < 1 ----- w is less than 1 Now "translate" the second one for me
October 16, 2014

Math
check if (2x+2)/(x+1) = (5x+1)/(2x+2) for ALL values of x that is, the equation should reduce to 0 = 0 to be a GS (I know it works for x = 3)
October 16, 2014

Calc
sorry, I forgot the +2xy on the left side should have been dy/dx = (y^3 - 2xy - 12x^2)/(x^2 - 3xy^2) I am disappointed that you could not find that simple error.
October 16, 2014

Calc
4x^3+x^2y-xy^3 = -4 we want derivatives with respect to x, so whenever we get a dx/dx, we get 1 So I will not write the dx/dx 's 12x^2 + (x^2)dy/dx + y(2x) - x(3y^2)dy/dx - y^3 = 0 dy/dx(x^2 - 3xy^2) = y^3 - 12x^2 dy/dx = (y^3 - 12x^2)/(x^2 - 3xy^2) check my work, I tend ...
October 16, 2014

math
correct
October 16, 2014

math
difference = 1/2 - 13/32 = 16/32 - 13/32 = 3/32
October 16, 2014

Calculus
or #1, use r^2 = x^2 + y^2 x^2 + y^2 = 169 2x dx/dt + 2y dy/dt = 0 , I differentiated with respect to t (time) or dy/dt = (-x/y)dx/dt when x = 12, dx/dt = 5 ft/s find dy/dt at that moment 12^2 + y^2 = 169 y = 5 dy/dt = (-12/5)(5) ft/s = -12 ft/sec the negative shows it is ...
October 16, 2014

Maths
y1/y2 = √x1/√x2 1/4 = √x1/√x2 √x2 = 4√x1 square both sides x2 = 16x1 x2/x1 = 16/1 or 1600 % e.g. suppose x = 36 then y = 6 now we want y to be quadrupled, so y = 24 and x would be such that √x = 24 , so x = 576 percentage increase in x...
October 16, 2014

Maths
6 men --- 4 hrs --- 6m deep 1 man ---24 hrs --- 6m deep 10 men 24/10 hrs -- 6 m deep 10 men 2.4 hrs --- 6 m deep 10 men 2.4/6 hrs --1 m deep 10 men .4 hrs ===1 m deep 10 men .4(5) hrs --- 5 m deep 10 men 2 hrs ---- 5 m deep OR it takes 24 manhrs to dig a 6 m deep hole it takes...
October 16, 2014

Math
1. looks like a GS, were a = 2/3, and r = 3 sum(5) = a(r^5 - 1)/(r-1) = (2/3)(3^5 -1)/2 = ..... 2. nope, (4x-2)/(2x) ≠ (6x-4)/(4x-2) for all values of x it would be true or only x = 1 3. 0.7575757575... = .75 + .0075 + .000075 + ... a GS where a = .75, r = .01 sum(...
October 16, 2014

maths
Suppose we had 25600 kg of food or 25600/80 kg per student for 80 days, or 1 kg per student for 1 day so in 20 days, 320(20) kg or 6400 kgwere used so 19200 kg are left for 300 students time for this to last = 19200/300 = 64 days or do the same with a variable let the amount ...
October 16, 2014

Map Rectangle
area on map = 12 cm^2 actual size of rectangle = 4000 cm by 3000 cm or 40 m by 30 m real area = 1200 m^2
October 16, 2014

math
-2/5x - 9 < 9/10 times 10 -4x - 90 < 9 -4x < 99 x > -99/4
October 16, 2014

Math
4cos^2 A - 3cosA = 0 cosA(4cosA - 3) = 0 cosA=0 or cosA = 3/4 but your domain is quadrant II, where the cosine is negative except cos90° = 0 so x = 90° do the 2nd the same way by factoring out tanA
October 15, 2014

Math
first of all, notice that each equation is divisible by 4 new equations: 8x + 9y = -4 9x + 8y = -4 multiply 1st by 8 ---> 64x + 72y = -32 multiply 2nd by 9 --> 81x + 72y = -36 subtract them 17x= -4 x = -4/17 into the 1st:8(-17/4) + 9y = -4 times 4 -136 + 36y = -16 36y = ...
October 15, 2014

St Grainne,s
let the tend digit be 2x then the unit digit and the hundreds digit are each x x+2x+x = 16 4x=16 x = 4 you are 484
October 15, 2014

maths
I will assume you meant to say that the area of the ink blot is growing at the rate of 2 cm^2 /s A = πr^2 dA/dt = 2πr dr/dt 2 = 2π (28/11) dr/dt dr/dt = 11/(28π) cm/sec = appr .125 cm/s
October 15, 2014

math
dozen of pencils --- x dozen of pens ----- y dozen of erasers --- z 4x + 3y + 2z = 16 2x + 4y + 6z = 90 6x + 2y + 3z = 70 Since you want it done by matrices, which for these nice equations would be overkill, I would find the inverse of 4 3 2 2 4 6 6 2 3 , then multiply that by...
October 15, 2014

Calculus I
or lim sin√x/e^x . clearly x≥0 use an intuitive approach. your numerator will be a number between -1 and 1, but your denominator keeps getting bigger and bigger so a relatively constant around ±1 divided by a huge number ---> 0 so lim x→ ∞ of ...
October 15, 2014

pre-calculus
This is very similar to the question you had before http://www.jiskha.com/display.cgi?id=1413245120
October 14, 2014

Math Check
for the 1st , I got -2 as the remainder for #2, did you mean (x^4 - 3x^2 + 2x - 1) / (x-1) ?? if so, then you are correct the way you had it would be one awful division.
October 14, 2014

math
if he spent 2/5 of it, then he has 3/5 of it left (3/5)x = 45 times 5 3x = 225 x = 75 His pocket money was $75
October 14, 2014

Geometry
Your symbols did not come out as you expected, but I concluded that you said: line BC bisects angle ABD, and angle ABC = 5x+11, angle CBD = 10x-4 so the two angles are equal, or 10x-4 = 5x+11 5x = 15 x = 3 check: angle ABC = 5(3) + 11 = 26 angle CBD = 10(3) - 4 = 26 YUP!!!
October 14, 2014

math
let sarah's sales be x then semir sold 3x and sung sold x+2
October 14, 2014

Math
cost of 3 pairs of shoes ---- x cost of handbag ---------- (1/2)x or x/2 x + x/2 = 324 times 2 2x + x = 648 3x = 648 x = 216 The 3 pairs of shoes cost $216 and the handbag cost $108
October 14, 2014

Math
ratio of games = 7x : 5x total games = 12x ration of games won : total games = 7x : 12x = 7:12
October 14, 2014

calculus
amount = 400(1/2)^(t/11.43), where t is number of days. so if t = 6 amount = 400(1/2)^(6/11.43) = 277.996 or appr 278 mg
October 14, 2014

math
done
October 14, 2014

math
1/2(x-2)<3/4(1-3x)<-2 preliminary: times 4 2(x-2) < 3(1-3x) < -8 2x - 4 < 3 - 3x < -8 2x-4 < 3-3x and 3 - 3x < -8 5x < 7 and -3x < -11 x < 7/5 and x > 11/3 no such number, thus no solution.
October 14, 2014

complex numbers
1. 4b-5t(-a-3)i=7-8i You don't say what you want. I see 3 variables in one equation, are you solving for one of them or what? 2. (7+4i) - (l+2i) is that supposed to say (7+4i) - (1+2i) ? then = 7+4i - 1 - 2i = 6 + 2i 3. (3+2i) (-2+4i) = -6 + 12i - 4i + 8i^2 = -6 + 8i - 8...
October 14, 2014

math prasad vk
1.2x = 2000 x = 2000/1.2 = .....
October 14, 2014

mathzzz preeshappd
Did you even look at how I did the same type of question for you just below ????
October 14, 2014

mathematiczzzzzz plzzzzzzzzzzzzzzz g
so manju spent 750 on the bike to make a profit of 15% on what she paid , she must sell it for 1.15(750) or 862.5 rupees
October 14, 2014

algebra
You did not define x I assume x represents the number of years since 1990 So for 1999 , x = 9 sub in 9 and evaluate YOur equation represents a parabola, find the vertex ... since the parabola opens up, there will be a minimum and a quick mental calculation will show that to be...
October 14, 2014

Math
1. "equilateral" means equal sides, but says nothing about its angles. How is regular defined ? 2. give yourself an example, e.g. consider a hexagon and an octogon, and see what happens 3. but the formula says 180(n-2) as the sum, so .... e.g. take a heptagon, n = 7...
October 14, 2014

maths
rate = distance/time = x km/20 min = 1000x m/1200 seconds = 5x/6 m/s
October 14, 2014

Math
1. let the number of sides be n each interior angle = 180(n-2)/n exterior angle = 360/n 180(n-2)/n = 3(360/n) + 20 times n 180(n-2) = 1080 + 20n 180n - 360 = 1080 + 20n 160n = 1440 n = 9 We have a 9-gon, which is called a enneagon or nonagon check: interior angle = 180(7)/9 = ...
October 14, 2014

maths
So you must select 3 or 4 women = C(8,3)*C(10,2) + C(8,4)*C(10,1) = 56(45) + 70(10) = 3220 check my arithmetic
October 14, 2014

math
assuming she went the same speed ... second trip/first trip = 4.75 rate/1.5 rate = 475/150 = 19/6 or appr 3.167 times as far
October 14, 2014

math
You could use Venn diagrams or use the formula: N(car OR cell OR married) = N(car) + N(cell)) + N(married) - N(car AND cell) - N(car AND married) - N(cell AND married) + N(car AND car AND married) =75+70+85-35 - 40 - 55 + 30 = 130 but there were 150 men considered, so 20 have ...
October 14, 2014

Finance
PV = 350(1.1)^-1 + 1000(1.1)^-3 + 1000(1.1)^-4 =
October 13, 2014

Math
both A and B are correct since they represent the same number 96 If the answer was supposed to be in scientific form, then B would be the correct choice, since the decimal must be after the first digit.
October 13, 2014

Math
hard to show in this format, since the numbers do not line up nicely 6 | 10 -50 0 0 -800 ...........60 60 360 2160 ..... 10 10 60 360 1360
October 13, 2014

math
case1 let a = .25, and b = .3 a+b = .55 which is < 1 case 2: let a = .8, and b = .7 then a+b = 1.5 which is NOT < 1 the statement should have been if a<1 and b< 1, then a+b < 2 (by adding the 2 inequalities)
October 13, 2014

Math
A, C, and D show a definite pattern of repetition, so they are rational B ??? hard to tell , perhaps there is a repetition further down I suspect the want you to say B
October 13, 2014

algebra
If the question was worded in that way, I would also have no clue .
October 13, 2014

Algebra
At 8:19 I posted this http://www.jiskha.com/display.cgi?id=1413243942 and showed you how to show exponents. You clearly did not even look at your previous post This question is the same type.
October 13, 2014

Math
scientific notation has a single digit number, followed by a decimal only A andB fit that property. look at the original number and compare it to A the decimal moved 8 places to the right, count them when you see 10^(negative) it represents a small number when you see 10^(...
October 13, 2014

Math
Did you count how many places the decimal point was moved? Then you must be sure of the answer.
October 13, 2014

Pre-Calc/Trig...
These are properties of a parabola that you absolutely MUST know to even be slightly successful in this topic. Giving you the answer will not help . Hint : make a quick sketch to see what the first one looks like for the second, why not sub in x = 0 as given in the point. Will...
October 13, 2014

math
treat the data as two ordered pairs, and find the linear equation (38, 2200) and (49,2125) slope = (2125-2200)/(49-38) = -75/11 so s - 2200 = (-75/11)(p-38) 11s - 24200 = -75p + 2850 11s + 75p = 27050 when s = 2143, 11(2143) + 75p = 27050 75p = 3477 p = $46.36 when s = 0 0 + ...
October 13, 2014

Calc: Related Rates
At a time of t seconds after noon, Jack will have walked 5t ft, while Jill will have walked 4t ft let the distance between them be d ft I see a right angled triangle with a base of 800-5t, a height of 4 t and a hypotenuse of d d^2 = (800-5t)^2 + (4t)^2 2d dd/dt = 2(800-5t)(-5...
October 13, 2014

Algebra
Use the following notation to show exponents x^2 - 4x - 19 = 13 x^2 - 4x - 32 = 0 (x-8)(x+4) = 0 take over.
October 13, 2014

inequalities
let's see when it IS 7 3x^3 + 4x^2 - 59x - 13 = 7 3x^3 + 4x^2 - 59x - 20 = 0 let's hope this factors nicely, tried: x = ±1, ±2, ±4, yup worked for x = 4 did synthetic division ... 3x^3 + 4x^2 - 59x - 20 = 0 (x-4)(3x^2 + 16x + 5) (x-4)(x+5)(3x + 1...
October 13, 2014

pre cal
if it does 2 rotations in 2 seconds, then it does 1 rotation in 1 second or 2π(13.5) inches per second = 2π(13.5)/12 ft /sec =7.06858.... ft/s (I stored in in my calculator memory for accuracy) = (7.06858...)/5280 miles / (1/3600) hr = appr 4.82 mph
October 13, 2014

Math
yes, according to the distance formula, the distance = √( (9-9)^2 + (-11 + 2)^2) = √(0 + 81) = √81 = 9
October 13, 2014

Calc
let the height of the balloon be h m then tanØ = h/60 , where Ø is the angle of elevation h = 60 tanØ dh/dt = sec^2 Ø dØ/dt when h = 30, dØ/dt = .1 rad/sec then tanØ = 30/60 = 1/2 hypotenuse = 30√5 secØ = 30√5...
October 13, 2014

typo - polar co ordinates
forgot the 4 in front of the 4cos^3 Ø should be x^2 + y^2 = 16x^3/(64r^3) - 3x/r x^2 + y^2 = (1/4)x/((x^2+y^2)√(x^2 + y^2)) - 3x/√(x^2+y^2)
October 13, 2014

polar co ordinates
the messy part is the cos (3Ø) we know cos 3Ø = 4cos^3 Ø - 3cosØ and since you know cosØ = x/r we get x^2 + y^2 = 16x^3/r^3 - 3x/r x^2 + y^2 = 16x/((x^2+y^2)√(x^2 + y^2)) - 3x/√(x^2+y^2) see: http://www.wolframalpha.com/input/?i=...
October 13, 2014

Buisness finance
simply solve 1(1.05)^t = 2 t log 1.05 = log 2 t = log2/log1.05 = appr 14.2 years
October 13, 2014

Math
and here is how http://www.jiskha.com/display.cgi?id=1413211761
October 13, 2014

Math
divide both sides by mg, where m ≠ g ≠ 0 sinA = ucosA u = sinA/cosA = tanA if A = 19° u = tan19 = appr .344
October 13, 2014

math
the cables form the hypotenuse of right-angled triangles for each one: h^2 = 15^2 + 8^2 = 289 h = 17 length of 2 such cables = 34 ft
October 13, 2014

alegbra
2a + b = 15.7 2(6.3) + b = 15.7 b = 3.1
October 13, 2014

maths.literacy
Assuming your tank is a cylinder, aren't you just asking for the area of a circle ? A = πr^2 and you know the radius. Just do the arithmetic
October 13, 2014

Probability
Choose 5 from 17 = C(17,5) = 17!/(5!12!) = 6188
October 13, 2014

algebra
You did not define what x nor F(x) represent. But that does not stop us from finding F(3) = (1/18)(3)^2 -1/12^3 + 1/2 = (1/18)(9) - 1/1728 + 1/2 = 1/2 - 1/1728 + 1/2 = 1 1/1728 or 1729/1728 whatevers (I have suspicions about the term 1/12^x , is it a typo ? ) 4.25 users ? don...
October 12, 2014

algebra
to get the next year's salary would multiply the previous year's salary by 1.07 in a GS, you would multiply the previous term by the common ratio of r. So what do you think?
October 12, 2014

statistics
since you are replacing the marble each time , and since most marbles don't have any memory that I know of, the prob is 19/38 or 1/2
October 12, 2014

Math
.08c = .12d 8c = 12d 2c = 3d c = 3d/2 then c+d = 3d/2 + d = 3d/2 + 2d/2 = 5d/2 or 2.5d in your specific case, you let c = 600 and d = 400 then c+d = 1000 , like you had now isn't 1000 = 2.5(400) or 2.5d ?
October 12, 2014

math
3x6 3x5 4x4 4x5 4x6 (5x3) -- already have it (5x4) 5x6 (6x3) (6x4) (6x5) 6x6 I see 7 of them
October 12, 2014

Algebra
I just noticed in the "Related Questions" below, that Steve noticed the same problem with the same question. I would strongly suggest that your coach (math-teacher) is mistaken.
October 12, 2014

Algebra
clearly this ball was thrown on this earth, or else your equation would have been h = 72t - 16t^2 I will assume you have a typo Your equation is a parabol. Do you know how to find the vertex of a parabola? I too am lost in trying to figure out your arithmetic. Did you decide ...
October 12, 2014

calculus
largest volume is obtained when the box is a cube so 6 faces total 60 square units each face is 10 square units so each side is √10 units long volume = (√10)^3 = 10√10 or appr 31.6 units^3
October 12, 2014

statistics
your data is perfectly suited for this webpage, which replaces the tables you probably have at the back of your text I got 15.87% http://davidmlane.com/hyperstat/z_table.html
October 12, 2014

@ Elena - Math
Do not tag a new question at the end of somebody else's question. It will appear to be a reply to that problem Yours: The sum so far is 80 after adding 10 the new sum is 90 avg of those 6 numbers = 90/6 = 15
October 12, 2014

Algebra: help!
You posted the same question yesterday as Rose . Very confusing if you change names http://www.jiskha.com/display.cgi?id=1413026488
October 12, 2014

Algebra 2 Answer Check
correct, you are looking at two parallel lines that will never meet
October 11, 2014

Math College (Algebra)
from the first; (3x - y)/(x^2 + y^2) = 3-x x^2 + y^2 = (3-x)/(3x-y) from the 2nd: (x+3y)/x^2 + y^2) = y x^2 + u^2 = (x+3y)/y (3-x)/(3x-y) = (x+3y)/y getting very nasty Wolfram says: http://www.wolframalpha.com/input/?i=solve+x+%2B+%5B%283x-y%29%2F%28x%5E2%2By%5E2%29%5D+%3D+3%...
October 11, 2014

Trigonometry
2cos^2 x - cosx - 1 compare to 2a^2 - a - 1 = (2a +1)(a - 1) , where a = cosx
October 11, 2014

Trigonometry
cos (2x) - cosx = 0 2cos^2 x - 1 - cosx = 0 (2cosx + 1)(cosx - 1) = 0 cosx = -1/2 or cosx = 1 if cosx = -1/2, then x = 120° or 240° x = 2π/3 or x = 4π/3 if cosx = 1 x = 0 or x = 2π x = 0, 2π/3 , 4π/3 , 2π
October 11, 2014

Trigonometry
the last equation that anonymus was looking at was sin (2x) = 1/2 so from our basic triangles and the CAST rule 2x = π/6 , 2x = π-π/6 or 5π/6 , ( 30° or 150°) then x = π/12 or x = 5π/12 but the period of sin 2x is π so by adding π...
October 11, 2014

math
Use a simple ratio 20/27.5 =12/x 20x = 12(27.5) 20x = 330 x = 330/20 = 16.5 or $16.50
October 11, 2014

math
is that supposed to be tan(75/2)°
October 11, 2014

Math
a) after 1 year --> 100000(1.1) after 2 years ---- 100000(1.1)^2 b) Aaron's --- > 99000/1.1 or 99000(1.1)^-1 c) what do you think?
October 11, 2014

equation
Anna: 20 km / 1 1/3 hr = 20000 m/80 min = 250 m/minute Julia: 100 m/10 min = 10 m/minute ????? I suspect a typo somewhere
October 11, 2014

Algebra
divide 19 1/2 by 3/4 = (39/2)(4/3) = 26 or 19.5/.75 = 26
October 11, 2014

Algebra, help please!!!
for each one, multiply each term by the LCM e.g. c: 5/6 - 2/3 x = 3/4 LCM = 12 so multiply each term by 12 (5/6)(12) - (2x/3)(12) = (3/4)(12) 10 - 8x = 9 -8x = -1 x = 1/8 do the others the same way in b) I would cross-multply first to get (1/3)x = 3/4 , the proceed by ...
October 11, 2014

another math equation
a statement such as a/4 = b/5 = 2/3 means that all fractions equal each other and are equal to 2/3 so set each one equal to 2/3 a/4 = 2/3 or a = 8/3 b/5 = 2/3 or b = 10/3 the ab = (8/3)(10/3) = 80/9 or 8 8/9
October 11, 2014

another math equation
if you mean a/4 = b/5 = 2/3, then do it the same way I just showed you for your previous post
October 11, 2014

math equation
type your fractions this way: a/4 = b/5 = 3 then: a/4 = 3 ---> a = 12 and b/5 = 3 --> b = 15 finally: a+b = 12+15 = 27
October 11, 2014

Math
are you not familar with the basic fundamental rules of solving equations. I "moved" the +7x from the left side of the equation to the right side of the equation or 7x - 6y -7x = -7x + 42 -6y = -7x + 42 now divide every term by -6 etc
October 8, 2014

Math
quick way: If the line is expressed in the form Ax + By + C = 0 the slope is -A/B , note the value of C does not enter the picture. so for 7x - 6y = 42 the slope is -7/(-6) = 7/6 or , by the usual grade 9 way 7x - 6y = 42 -6y = -7x + 42 y = -7x/-6 + 42/-6 y = (7/6)x - 7 ,,,, ...
October 8, 2014

Calculus
let the side parallel to the canyon wall be y ft let each of the other two shorter and equal sides be x 2x + y = 500 y = 500-2x area = xy = x(500-2x) = 500x - 2x^2 since you labeled it Calculus d(area)/dx = 500 - 4x = 0 for a max of area 4x = 500 x = 125 when x = 125 , y = 500...
October 8, 2014

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