<PRE><B>Question 697544</B>
Add their rates of moving cans to get
their rate moving them together.
1st belt:
Rate = ( 400 lbs of cans ) / ( 5 min )
2nd belt:
Rate = ( 400 lbs of cans ) / ( 9 min ) 
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Let {{{ t }}} = time in minutes to move 
400 cans with both belts used
Call 400 cans &quot; 1 job &quot;
{{{ 1/5 + 1/9 = 1/t }}}
Multiply both sides by {{{ 45t }}}
{{{  9t + 5t = 45 }}}
{{{ 14t = 45 }}}
{{{ t = 3.2143 }}} min
Both belts can move 400 cans in 3.2143 min
check:
{{{ 1/5 + 1/9 = 1/t }}}
{{{ .2 + .1111 = 1/3.2143 }}}
{{{ .3111 = 1/3.2143 }}}
{{{ 1.0000044 = 1 }}}
OK- error due to rounding off
</PRE>