## anonymous 4 years ago Twin brothers, Billy and Bobby, can mow their grandparent's lawn in 76 minutes. Billy could mow the lawn by himself in 15 minutes less time than it would take Bobby. How long would it take Bobby to mow the lawn by himself?

1. amistre64

T(bob) + T(bill) = 76 is what im thinking

2. amistre64

bob-15 + bob = 76

3. amistre64

2bob = 91 bob = 91/2 = 45.5 maybe

4. amistre64

that almost feels right; almost ...

5. amistre64

the by himself part is not being taken into account

6. anonymous

amistre 64 ineed ur help

7. amistre64

I dont know c++

8. anonymous

oh....ok...:(

9. amistre64

if we had the set up the we know bob and bill alone we could get to time together .... so im gonna have to look backwards at this :)

10. amistre64

bob = time (b) alone bill = time (b -15) alone $\frac{1}{b}+\frac{1}{b-15}=\frac{1}{76}$ $\frac{b-15}{b(b-15)}+\frac{b}{b(b-15)}=\frac{1}{76}$ $\frac{b-15+b}{b(b-15)}=\frac{1}{76}$ $\frac{b(b-15)}{b-15+b}=76$ $\frac{b^2-15b}{2b-15}=76$ $b^2-15b=76(2b-15)$ $b^2-15b-76(2b-15)=0$ $b^2-15b-152b+1140=0$ $b^2-167b+1140=0$ maybe?

11. amistre64

b = about 160 or 8; so id go with 160 minutes as a gut thing if:$\frac{1}{160}+\frac{1}{160-15}=\frac{1}{76}$then it should be good

12. amistre64

http://www.wolframalpha.com/input/?i=1%2F160+%2B+1%2F%28160-15%29+-+1%2F76 yeah, im going with that, or close to it