Tuesday
September 30, 2014

Posts by Reiny


Total # Posts: 27,193

math
correct
May 25, 2014

math
I assume you meant (x+2)/2 = 4/x multiply each side by 2x , (sometimes called cross-multiplying) x^2 + 2x = 8 x^2 + 2x - 8 = 0 (x+4)(x-2) = 0 x = -4 OR x = 2 , which is choice 2) (if the way they presented the answer used the word AND, they they are technically incorrect. x ...
May 25, 2014

Math - Personal Finance
To use the formula for a series of payments, such as carpayments, and mortgages, the period of compounding and the period of payments must be the same. Yours has the interest compounded semi-annually, and the payments are monthly, which does not match up So we have to find the...
May 25, 2014

math
looks like tan Ø = 169/500 = .338 Ø= appr 19°
May 25, 2014

Algebra 1
dh/dt = -32t + 148 = 0 for a max of h 32t = 148 t = 148/32 = 4.625 when t = 4.625 h = -16(4.625)^2 + 148(4.625) + 3 0 = 372.25 looks like d
May 23, 2014

Algebra
I think you are referring to one of the alternate ways to represent a combination see: http://laurashears.info/math122/unit5/notation/ Steve found the value of each of your combinations, so just multiply them 84*15*3 = .......
May 22, 2014

Geometry
I will assume you meant (x + 6)^2 + (y + 4)^2 = 36 , ( notice how the exponent is shown ) which is a standard equation of a circle with centre at (-6,-2) and a radius of 6 units Just noticed that I answered the same question back in 2012 http://www.jiskha.com/display.cgi?id=...
May 22, 2014

Algebra 2
I will assume that your light is parabolic and the bulb is placed at its focal point The standard form of the equation with vertex at the origin and focal point (p,0) is y^2 = 4px so you have a focal point of (6,0) then y^2 = 24x is our equation if the diameter is 36 inches, ...
May 22, 2014

HELP!!!! MATH
Did you make your sketch? If the depth is y you should see that h/24 = cos15° h = 24cos15 = appr 23 ft
May 22, 2014

math
number of participants --- x number passed first part = 7x/8 (failed = 1/8, so passed = 7/8) number who passed 2nd test = (2/7)(7x/8) = (1/4)x so 1/4 of the original passed the exam check: suppose 56 took the test so 49 passed of those (2/7)(49) or 14 passed 14/45 = 1/4
May 22, 2014

math
let the number of red marbles be x number of green marbles = (1/3)x = x/3 yellow marbles = 6x red : green : yellow = x : x/3 : 6x = 3x : x : 18x for a total of 24x so yellows would be 18x/24x = 3/4 of his collection
May 22, 2014

geometric
Next time you are near a big truck, you will notice that most of the trailers will have the notation 53' written along the side, showing that the standard length of the trailer is 53 feet. It asked for the customary way, so it is feet.
May 22, 2014

calculus
Wolfram amazes me more every day. http://www.wolframalpha.com/input/?i=area+between+y%3D+ln%281-x%29+%2C+y%3D3+%2C+x%3D0 notice that Damon took horiontal slices, while Wolfram took vertical slices. Same result of course.
May 22, 2014

math
So the length of the base of the continuous rectangle = 10(2) + 10(4) = 60 inches so the distance around the whole thing = 2(60) + 2(3) = 126 inches
May 22, 2014

trig
make a sketch to see that sin10° = height/35 height = 35sin10 = appr 6.1 ft
May 22, 2014

math
Let the distance run by the dog be 7x m let the distance run by the cat be 4x m so 7x = 4x + 12 3x = 12 x = 4 So the dog has to run 7(4) or 28 m to catch the cat. check: In the same time that the dog ran 28 m , the cat ran 16 m but the cat had a 12 m head-start , giving us ...
May 22, 2014

Algebra where did I go wrong
Mark, the correct answer is 10 Please trust Damon.
May 22, 2014

Algebra
prob (2 yellow) = (6/15)(6/15) = 36/225 = 4/25 Since you are returning the first marble picked, the second probability is the same as the first one.
May 21, 2014

Precalculus
I followed your description ok. so we get: -8 + 2x + 15 = 9 2x = 2 x = 1 10 + 3x + 25 = 38 3x = 3 x = 1 , confirming our first answer 4 - 3x + 5 = y 4-3+5=y y = 6 So x = 1 , y = 6
May 21, 2014

algebra
let d be the number of DVD's rented 2d + 6 = 48 2d = 42 d = 21 If the customer borrows less than 21 DVD's the first plan is better If the customer borrows 21 DVD's s, the cost is the same If the customer borrows more than 21, the flat rate of $48 is best.
May 21, 2014

math (last question #5) @Damon
if c is 8y^2 - 10y + 3 , then yes.
May 21, 2014

Math 8th gr.
27 - (-9) (-2) ÷ 3 * (-4) - 0 - 33 - (-39) just follow the rule of operations ... 27 + 24 - 0 - 33 + 39 = 57
May 21, 2014

MATH
makes no sense. We don't know the distribution of boys to girls in the 12 middle schoolers.
May 21, 2014

maths
yes, what about it? The statement is true.
May 21, 2014

math test
Pacific = x Caribbean = x+32 Medi = 4x - 38 x+x+32+4x-38 = 828 you solve it, it is easy
May 21, 2014

Calculus
so one side is not needed. let the two width be x m let the one length be y m 2x + y = 1000 y = 1000 - 2x area = xy = x(1000-2x) =1000x - 2x^2 d(area)/dx = 1000 - 4x = 0 for a max of area 4x = 1000 x = 250 y = 1000-500 = 500 max area = xy = 250(500) = 125000 m^2
May 21, 2014

Calculus
dd/dt = 1200 - 72000t = 0 for a max 72000t = 1200 t = 1/60 d = 1200(1/60) - 36000(1/3600) = 10 m
May 21, 2014

Algerbra 2
ummhhh, value in 6 years = 118000(1.09)^6
May 20, 2014

Algerbra 2
value in 6 years = 118000(1.09)^6 = ....
May 20, 2014

Algebra
total = 2x+1 + 3x + x+2 = 6x + 3 prob red = (2x+1)/(6x+3) = (2x+1)/(3(2x+1) ) = 1/3
May 20, 2014

math
FF -- x DD -- y RR -- z x+y+z = 41.70 , #1 2x + z = 37.95 , #2 x+y = 26.75 , #3 #1 - #3" z = 14.95 sub into #2 2x + 14.95 = 37.95 2x = 23.00 x = 11.50 sub into #3 11.50 + y = 26.75 y = 15.25 FF costs 11.50 DD costs 15.25 RR costs 14.92
May 20, 2014

Math
your slope of -2/5 or -.4 for line AB is correct The slope of a line can be any real number, both positive and negative If the slope is positive the line leans to the right If the slope is negative the line leans to the left if the slope is zero, the line is horizontal.
May 20, 2014

Precalculus
Since you are given the slope and the y-intercept, the problem becomes a matter of just subbing in the values y = (5/8)x + 4
May 20, 2014

Algebra
19 P 2 = 19!/(19-2)! = 19(18)(17!)/(17! = 19(18) = 342 If by "if there is no r" you mean "if the value of r = 0" then 4P0 = 4!/(4-0)! = 1
May 20, 2014

Algebra
Damon, I think you forgot to divide by 7 before taking the square root. SD = √(80/7) = 3.3806 The amazing Wolfram supports this http://www.wolframalpha.com/input/?i=standard+deviation+4%2C+8%2C+5%2C+12%2C+3%2C+9%2C+5%2C+2
May 20, 2014

geometry
So you need the length of the hypotenuse sin 13° = 186/x x = 186/sin13° = 826.8 ft
May 20, 2014

algebra
width --- x length -- 2x+4 x(2x + 4) = 400 2x^2 + 4x = 400 x^2 + 2x = 200 x^2 + 2x + 1 = 200 + 1 (x+1)^2 = 201 x+1 = ± √201 x = -1± √201 x = appr 13.18 cm or a negative, which we will reject The width is appr 13.2 and the length is appr 30.4
May 20, 2014

math homework help
PV = 125000(1.03)^-5 = $107,826.10
May 20, 2014

Math: Linear Equation
A linear equation of your type will produce a straight line when graphed. So all you need are 2 distinct points. Using the x and y intercepts are a quick and easy way to do this, after all the intercepts are just plain ol' points. Here is an easy way to do this: let x = 0 ...
May 20, 2014

math
distance = 7(55) miles = 385 miles number of gallons of gas = 385/30 = appr 12.8 or 13 gallons
May 20, 2014

no
3 undecillion http://www.thealmightyguru.com/Pointless/BigNumbers.html in scientific notation: 3.0 x 10^36 A rather large number, considering that the total number of grains of sands are estimated to be only about 7.5 x 10^18 and Carl Sagan claimed that there are more stars in...
May 20, 2014

Math
I even tried this to see the median answer http://www.wolframalpha.com/input/?i=sort+19%2C+19%2C+14%2C+14%2C+16%2C+19%2C+19%2C+16%2C+16%2C+15%2C+17%2C+16%2C+17%2C+16%2C+15%2C+14%2C+15%2C+15%2C+17%2C+14%2C+16%2C+15
May 20, 2014

Math
Wow, I didn't know that Wolfram does even this stuff This wonderful webpage amazes me more all the time. http://www.wolframalpha.com/input/?i=mean+19%2C+19%2C+14%2C+14%2C+16%2C+19%2C+19%2C+16%2C+16%2C+15%2C+17%2C+16%2C+17%2C+16%2C+15%2C+14%2C+15%2C+15%2C+17%2C+14%2C+16%2C+...
May 20, 2014

statistics
prog(right) = 1/5 prob(wrong) = 4/5 prob of your stated event is, getting none right --> C(12,0)(1/5)^0 (4/5)^12 = .0687 getting one right --> C(12,1) (1/5) (4/5)^11 = .20616 getting two right --> C12,2) (1/5)^2 (4/5)^10 = .2835 getting three right --> C(12,3) (1/5...
May 20, 2014

Algebra
z-score = (given value - mean)/sd -1.7 = (13 - 18.1)/sd -1.7sd = -5.1 sd = -5.1/-1.7 = 3
May 19, 2014

Need help with pre cal hw
1. I sketched a triangle, and noticed I could use the cosine law: R^2 = 8^2 + 6^2 - 2(8)(6)cos 50° = 38.2923... R = appr 6.189 km or use vectors first vector = (8cos30 , 8 sin 30) = (6.9282 , 4) 2nd vector = (6cos160, 6sin 160) = (-5.63815.. , 2.05212) sum = ( 1.29004...
May 18, 2014

math
a reflection across the y-axis causes the x value to become opposite, while the y stays the same using your wording: (x,y) ----> (-x + 1, y - 2) A(1 , -3) ----> A' (0, -5) B(4 , -5) ----> B' (-3 , -7) C(3 , -1) ----> C' (-2 , -3) You should really have ...
May 18, 2014

RE-TYPE
Oh no, log6 is not a number, it is an operator. You can't factor out log6 (that would be doing something like √8 - √3 = (√)(8-3) ) You have to use your rules of logs. log6(x+3) - log6(x-5) = 2 log6 ( (x+3)/(x-5) ) = 2 which by definition is (x+3)/(x-5) = ...
May 18, 2014

Calculus
Oh no, 6 is not a number, it is an operator. You can't factor out 6 (that would be doing something like √8 - √3 = (√)(8-3) ) You have to use your rules of logs. 6(x+3) - 6(x-5) = 2 6 ( (x+3)/(x-5) ) = 2 which by definition is (x+3)/(x-5) = 6^2 = 36 36x - ...
May 18, 2014

Calculus
log5 16807^5 - log57^3 = log5A log5 (16807^5/7^3) = log5A A = 16807^5 / 7^3 = 49(16807)^4 = appr 3.91 x 10^18
May 18, 2014

maths
I strongly recommend that you mind your p's and q's
May 18, 2014

Calculus
The way you typed R(t), we have to read it as R(t) = 9/2.718 ( t(t-3)^3) then R' (t) = (9/2.718) [ t (3)(t-3)^2 + (t-3)^3 ] = (500/151)(t-3)^2 ( 3t + t-3) = (500/151)(4t - 3)(t-3)^2 How did the base of (t-3) suddenly turn into (t-4) ?
May 17, 2014

algebra
balance on home = .08(118,000) = $94,400 i = .095/12 = .00791666... n = 30(12) = 360 paym( 1 - 1.00791666..^-360)/.00791666.. = 94400 payment = $793.77
May 17, 2014

algebra
a) since 0% interest, the monthly payment would simply be 42500/60 = $708.33 b) I believe in the US , add-on-interest is done this way: amount to be financed = 42500-5100 = 37400 interest = 37400(.025)(5) = 4675.00 total of loan = 37400 + 4675 = 42075.00 monthly payment = ...
May 17, 2014

math
Unfortunately , the expression and measurement of time is not metric, so we have to make some changes. (similar to the US method of working in miles, yards, feet and inches) (14 hrs, 3 min)/3 = (13 hrs, 63 min)/3 = 4 1/3 hrs, 21 minutes = 4 hrs, 20 min , 20 min = 4 hrs and 41 ...
May 17, 2014

math
Does it fit the description I gave you? How about some thinking on your part after all your posts ?
May 17, 2014

math
in a reflection in the x-axis, all the x values stay the same, but the new y's become opposites of the old ones now, which matches that description.
May 17, 2014

math
prob(under 25) = .55 prob(over 25) = .45 prob (exactly 4 of 6 are under 25) = C(6,4) (.55)^4 (.45)^2 = .27795
May 17, 2014

Math
(-8x)(3x^2) = -24x^3
May 17, 2014

math
10 ---> 1 , looks like it went left 9 3 ---> 6 , looks like it went up 3
May 17, 2014

math
just evaluate y for the given x's and plot the points e.g , when x = -2 y = (1/3)(2) - 2 = 2/3 - 2 = -4/3 ------> so you have the point (-2, - 4/3
May 17, 2014

math
Actually I just noticed your equation is not quite clear. is the exponent 3 ? then you would have written it as y = 2x^3 or did you forget to type the exponent ? It would be highly unusual for a text to put the + sign in front of the exponent like you typed it.
May 17, 2014

math
evaluate the y for the given x's, then plot the points. Join them with a smooth curve. You will get a parabola
May 17, 2014

Math
Assuming your ã is √ #3 , the -11√8 becomes -22√2 the rest are correct
May 17, 2014

alegbra/stressed
in each case you divide the rate by the annual compounding frequence, and multiply the years by that annual compouding frequency e.g. if compounded quarterly, the annual compounding frequencey is 4 I will do that one, you try the others. 6.9 %> compounded quarterly i = .069...
May 17, 2014

Math
I think we should use compound interest here. i = .09/12 = .0075 let the payment be p p( 1 - 1.0075^-36)/.0075 = 100000 p = $3179.97
May 17, 2014

Chemistry, not Math
label your problem using the right subject
May 17, 2014

math
for the 1st pair, since you know what y is , just plug that value into the first equation and solve for x #2: 3x - 14y = 0 x - 4y + 1 = 0 3x - 14y = 0 multiply the 2nd by 3 3x - 12y = -3 subtract them -2y = 3 y = -3/2 sub into x - 4y = -1 x - 4(-3/2) = -1 x + 6 = -1 x = -7 x...
May 17, 2014

math
4(2x-9)-4x= 4-6x 8x - 36 - 4x = 4 - 6x 10x = 40 x = 4 16y plus 4 =-10 16y + 4 = -10 Does your keyboard not have a + sign? 16y = -14 y = -14/16 = -7/8
May 17, 2014

Math
it is called a subscript it is not an actual mathematical operator, but instead is an indicator. e.g. you often see it to label two points (x1 , y1) and (x2 , y2) to state that you have two points of the form (x,y) but the x's and y's are different e.g. if you have two...
May 17, 2014

maths
What does "works up to" mean in mathematics ????
May 17, 2014

Math
942!/(15n) = 942x941x940x939x938!/(15n) = 942(941)(188)(313)(938!)/n I divided by 5 and by 3 leaving the division by n
May 17, 2014

Math
multiply top and bottom by √6 + √3 (2 √ 6 + √ 3)/ ( √ 6- √ 3) * (√6 + √3)/(√6 + √3) = ( 12 + 3√18 + 3)/(6-3) = (15 + 9√3)/3 = 5 + 3√2
May 17, 2014

Calc Help Please Again Last one!
I will split it up for you ... (6x-58)/( (x+9)(x-7) ) let A/(x+9) + B/(x-7) = (6x-58)/( (x+9)(x-7) ) A(x-7) + B(x+9) = 6x - 58 let x = 7 0 + 16B = -16 B = -1 let x = -9 -16A + 0 = -112 A = -7 so .... (6x-58)/( (x+9)(x-7) ) = -7/(x+9) - 1/(x-7) now it integrates easily using ln...
May 16, 2014

Calc Help Please Again!
can't tell if your equation is y = e^(x+4) or y = e^x + 4 , why is there a 1 in front of the x ?
May 16, 2014

Calc Help Please
I got (1/4) (ln(x-2) - ln(x+2) ) + c how did your x-2 from the original denominator turn into 2-x) I used partial fractions
May 16, 2014

Geometry
make a sketch to see that height/36 = tan 25° height = 36tan25 = appr 16.8 ft
May 16, 2014

Algebra
yes
May 16, 2014

alegbra
my equation, (very close to yours) 225500 = PV e^(8.4246575(.0855)) 225500 = PV e^(.720308219) , now press 2nd ln 225500 = PV (2.055066524) PV = 109,728.81 I let the calculator carry all the decimal places and only rounded off my final answer to the nearest cent. You were off ...
May 16, 2014

math
distance = √( (-3-8)^2 + (-10+10)^2) = √(121 +0) = √121 = 11 We can see this without any calculation. Since the x values are the same for both points, the line is a vertical one. So all we have to do is take the difference between -3 and 8 , which is 11
May 16, 2014

math
number of $5 tickets --- x number of $10 tickets --- y number of $15 tickets ---- 180-x-y x + (180-x-y) = 2y x + 180 - x - y = 2y 180=3y y = 60 income equation: 5x + 10y + 15(180-x-y) = 1900 5x + 600 + 15(120-x) = 1900 5x - 15x + 600 + 1800 = 1900 -10x = -500 x = 50 x=50 y=60 ...
May 16, 2014

math(compound interest )
What you wanted as an equation is ... [ x( 1 + .1/360)^20 - 600 ](1+.1/360)^108 = 8900 x(1+.1/360)^20(1+.1/360)^108 - 600(1+.1/360)^108 = 8900 x((1.00557024)((1.03045024) - 618.2701442 = 8900 x(1.036190095 = 9518.270144 x = 9185.83
May 16, 2014

math trigonometry
I don't understand your question. Are we looking at two different equations ? Are we solving 10 sec Ø + 13sinØ = 0 and 5tan Ø - 12 = 0 ???? or .... ? is (0,90°) the domain?
May 15, 2014

Algebra 1
first equation: -2x - 2y = 4 ----> x+y = -2 2nd equation: 2y = -2x - 4 2x + 2y = -4 x + y = -2 looks like they are the same line, so you have one line any ordered pair that works in one of them, will work in the other. There will be an infinite number of solutions.
May 15, 2014

Math-- Ms. Sue??
#1 , wrong. If you plot your points you will see that it is (8,5) notice that now two pairs of points have the same x , making the lines vertical, and 2 pairs of points have the same y, making the horizontal. #2, ok #3, ok #4, your answer: (5,-4) and (-2,1) -- slope = (1-(-4...
May 15, 2014

Math
prob(brown, then violet) = (8/16)(1/16) = 1/32
May 15, 2014

Math - Int Trig
y = √x shift up 4 units -----> y = √x + 4 reflect about the y-axis ---> y = √-x + 4 , for x ≤ 0 shift right 2 units -----> y = √(-(x-2)) + 4 , x≤2 again, Wolfram verifies this http://www.wolframalpha.com/input/?i=y+%3D+√%28-%...
May 15, 2014

Math - Int Trig
start: y = |x| shifted right : y = |x-3) stretched by factor of 3 : y = 3|x-3| vertically down 2: y = 3|x-3| - 2 reflected about x-axis y = -3|x-3| + 2 behold the wonders of Wolfram http://www.wolframalpha.com/input/?i=y+%3D+%7Cx%7C+%2C+y+%3D+%7Cx-3%7C+%2C+y+%3D+3%7Cx-3%7C+%2C...
May 15, 2014

math
multiply each of the prob. answers I just gave you by 100
May 15, 2014

math
Four possible outcomes: HH HT TH TT prob(HH) = 1/4 prob(TT) = 1/4 prob (TH or HT) = 2/4 = 1/2 notice the 3 answers add up to 1, since one of those possibilities must happen
May 15, 2014

Geometry
(-3,-1) ---- dilation factor of 2 ----> (-6, -2) show it by plotting the two points how does the distance to the origin change ?
May 15, 2014

Algebra 1
looks like f(3) = 2 then g( f(3) ) = g(2) = -3
May 15, 2014

Trig 3
sloppy way of writing the trig expressions ( when you write tan2, you are asking for the tan(2 radians. What you meant was something like tan^2 Ø It has to be the sine of something, the cosine of something, or the tangent of something. anyway ..... (1 - cos^2 Ø)/...
May 15, 2014

Geometry
Any regular n-gon can be changed to n isosceles congruent triangles by drawing all radii to the vertices of the polygon. the area of a triangle = (1/2)(base)(height) the area of one of these = (1/2)(side)(apothem) where the apothem is the distance from the centre of the ...
May 15, 2014

math(compund interest )
Major Hint: Did you notice that from 16 April to 16 Oct is 6 months? So your time can be very easily expressed in half-years, and quarter-years. From all the knowledge you have gained by having received many answers for similar questions to the above, you should now be able to...
May 15, 2014

mathematics for management
NO you used the concept of continuous compounding but it said it was compounded monthly Even with the above in consideration your expression of 8888(e^0.06(0.25)) makes absolutely no sense. i = .06/12 = .005 n = 3(12) = 36 months PV = 8888(1.005)^-36 = $7427.21 For a single ...
May 15, 2014

math
How do you expect us to know what table you are working from. With today's excellent scientific calculators, the use of "tables" that were found in the back of most textbooks in the past is no longer common practise. Your question is simply PV = 100000(1.05)^-50...
May 15, 2014

math
what is 20000(1.06)^15 ?
May 15, 2014

math(urgent)
Just use the formula. Amount = payment( (1+i)^n -1)/i Amount = 1000(1.08)^3 -1)/.08 = 3246.40
May 15, 2014

Trig
3x^2 + 4y^2 = 12 divide by 12 x^2/4 + y^2/3 = 1 we know sin^2 t + cos^2 t = 1 so sin^2 t = x^2/4 = (x/2)^2 ---> sin t x/s ----> x = 2sin t and cos^2 t = y^2/3 = (y/√3)^2 cos t = y/√3 ----> y = √3cos t x = 2sint y = √4cost confirmation: http://...
May 14, 2014

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