Question 824343
Let {{{ t }}} = the time in hours for the new auditor
to check a bank's deposits
An experienced bank auditor can check a bank's 
deposits in {{{ t/2 }}} hours
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( 1 job / t hrs ) = the new auditor's rate of working
( 1 job / t/2 hrs ) = experienced auditor's rate of working
( 1 job / 4 hrs ) = their rate working together
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Add their individual rates to get their rate working together
{{{ 1/t + 1/((t/2)) = 1/4 }}}
{{{ 1/t + 2/t = 1/4 }}}
Multiply both sides by {{{ 4t }}}
{{{ 4 + 8 = t }}}
{{{ t = 12 }}} hrs
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The experienced auditor's rate is:
{{{ 2/t = 2/12 }}}
{{{ 2/t = 1/6 }}}
The experienced auditor's rate is ( 1 job ) / ( 6 hrs ),
so it takes 6 hrs to check the bank