Question 942153
Let {{{ R }}} = the rate of working of the slow man
{{{ 2R }}} = the rate of working of the two faster men
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Add their rates of working to get rate working together
{{{ R + 2R + 2R = 1/56 }}}
{{{ 5R = 1/56 }}}
{{{ R = 1/280 }}}
{{{ 2R + 2R = 2/280 + 2/280 }}}
{{{ 4R = 4/280 }}}
{{{ 4R = 1/70 }}}
It takes 70 hrs for the 2 faster men digging together
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check:
{{{ 5R = 1/56 }}}
{{{ 5*(1/280 ) = 1/56 }}}
{{{ 1/56 = 1/56 }}}
OK