Question

Please need help with a word problem

Answer 1

It takes Brian 15 hours longer to build a model car than it takes John. If they work together they can build one on 4 hours. Using complete sentences, explain the steps in figuring out how to determine the time it would take Brian to build the car on his own. So if together they are 1/4 and Brian is 1/15x am I going in the right direction?

Answer 2

b = j+15 is given

1 job = 4 hours = j+b

Answer 3

so, if j+b can do 1/4 of the job in one hour

j+j+15 = 1/4 of the job per hour

2j + 15 = 1/4 per hour

Answer 4

ok very different from my book mine is more like 1 for numerator equals job 4 equals # of hours for both to complete. it would be the 1/4 less the 1/15x to determine the 1/x of the unknown?????

Answer 5

the per hour is a bad thought on my part ...

2j hours + 15 hours = 4 hours is what we should prolly be addressing

2j+15 = 4, and this is going negative ....

Answer 6

if we do this by hourly rates of work
\[\frac{1}{b}+\frac{1}{j}=\frac{1}{4}\]

\[\frac{1}{j+15}+\frac{1}{j}=\frac{1}{4}\]
\[\frac{j+j+15}{j(j+15)}=\frac{1}{4}\]
\[4(2j+15)=j^2+15j\]

Answer 7

\[j^2+7j-60=0\]\[j=\frac{-7+\sqrt{49-4(-60)}}{2}\]
j = 5 from that

Answer 8

holy crap

Answer 9

lol, right or wrong?

Answer 10

I was following you right up to the point of how to figure out the equation! This is above my paygrade! If I turn it in they will know I didn't do it myself :)

Answer 11

quadratic formula ...

Answer 12

\[ax^2+bx+c=0~:~x=\frac1{2a}(-b\pm\sqrt{b^2-4ac})\]

Answer 13

yep I got that just didn't know how you got from the equation to it. As u can tell not a math person is y I am here. I stopped at 2x+15/x(x+15=1/4

Answer 14

"cross multiply" to get it out of fraction mode

Answer 15

ok that really a lot thank you!!!!

Answer 16

your welcome

Answer 17

Is it possible to solve an equation if your denominator is zero? isn't that just an extraneous solution?