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anonymous

  • 4 years ago

A motorboat can go 8miles downstream on a river in 20mins.It takes 30mins for the boat to go upstream the same 8miles.find the speed of the current. A.20mph B.16mph C.24mph D.4mph

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  1. Mertsj
    • 4 years ago
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    |dw:1328114685991:dw|

  2. anonymous
    • 4 years ago
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    |dw:1328125751197:dw|

  3. Mertsj
    • 4 years ago
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    \[\frac{1}{3}(r+c)=8\] \[r+c=24\] \[r-c=16\]

  4. Mertsj
    • 4 years ago
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    Add the two equations.

  5. Mertsj
    • 4 years ago
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    \[2r=40\] \[r=20, r+c=24, c=4\]

  6. anonymous
    • 4 years ago
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    D. The current speed is 4 mph. Let r and c be the speed of the boat and current respectively. Minutes have been converted to hours. Solve the following for r and c:\[\left\{(r+c)\frac{1}{3}=8,(r-c)\frac{1}{2}=8\right\} \]\[\{r=20,c=4\} \]

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