Thursday

October 23, 2014

October 23, 2014

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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