Question 720385
Add their rates of raking
Heather's rate:
( 1 yard ) / ( 4 hrs )
Beth's rate
( 1 yard ) / ( 6 hrs )
Rate raking together:
( 1 yard ) / ( t hrs )
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{{{ 1/4 + 1/6 = 1/t }}}
Multiply both sides y {{{ 12t }}}
{{{ 3t + 2t = 12 }}}
{{{ 5t = 12 }}}
{{{ t = 2.4 }}} hrs
{{{ .4*60 = 24 }}}
Together, they can rake the yard in 2 hrs 24 min
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check:
{{{ 1/4 + 1/6 = 1/t }}}
{{{ .25 + .1666 = 1/2.4 }}}
{{{ .25 + .16666 = .41666 }}}
{{{ .41666 = .41666 }}}
OK