Question 793804
Add their rates of baking to get their rate working together
Maria's rate: 
( 5 cakes ) / ( 3 hrs )
Amy's rate:
( 5 cakes ) / ( 2 hrs )
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Let {{{ t }}} = time in hrs for them to bake 
{{{ 6 }}} cakes working together
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{{{ 5/3 + 5/2 = 6/t }}}
Multiply both sides by {{{ 6t }}}
{{{ 10t + 15t = 36 }}}
{{{ 25t = 36 }}}
{{{ t = 1.444 }}}
{{{ .444*60 = 26.4 }}}
It will take them 1 hour and 26 minutes working together