Question 1122729
B, boy's rate
G, girl's rate
RT=W, rate time work


{{{system((4B+10G)*5=1,B=(5/4)G)}}}


{{{(4*(5/4)G+10G)*5=1}}}


{{{(5G+10G)*5=1}}}


{{{75G=1}}}


{{{G=1/75}}}-------one girl can dig 1 hole in 75 hours.


{{{B=(5/4)(1/75)}}}

{{{B=(1)/(4*15)}}}

{{{B=1/60}}}---------one boy can dig 1 hole in 60 hours.


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How many boys will be needed to dig the hole in 3 hours?
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n boys;
{{{n(1/60)*3=1}}}


{{{n=60/3}}}

{{{highlight(n=20)}}}