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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?

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  1. amistre64
    • 4 years ago
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    T(bob) + T(bill) = 76 is what im thinking

  2. amistre64
    • 4 years ago
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    bob-15 + bob = 76

  3. amistre64
    • 4 years ago
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    2bob = 91 bob = 91/2 = 45.5 maybe

  4. amistre64
    • 4 years ago
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    that almost feels right; almost ...

  5. amistre64
    • 4 years ago
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    the by himself part is not being taken into account

  6. anonymous
    • 4 years ago
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    amistre 64 ineed ur help

  7. amistre64
    • 4 years ago
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    I dont know c++

  8. anonymous
    • 4 years ago
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    oh....ok...:(

  9. amistre64
    • 4 years ago
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    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
    • 4 years ago
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    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
    • 4 years ago
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    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
    • 4 years ago
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    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

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