Question 1069062
This is actually a "work" problem
Alvin's rate of working:
[ 1 invitation ] / [ 13 sec ]
Geraldine's rate of working:
[ 1 invitation ] / [ 40 sec ]

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Let {{{ t }}} = time in sec to address
140 invitations
Their rate working together:
[ 140 invitations ] / [ t sec ]
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Add their rates of working to get their
rate working together
{{{ 1/13 + 1/40 = 140/t }}}
Multiply both sides by {{{ 13*40*t }}}
{{{ 40t + 13t = 13*40*140 }}}
{{{ 53t = 72800 }}}
{{{ t = 1373.58 }}} sec
Convert this to minutes
{{{ 1373.58 / 60 = 22.893 }}} min
Convert the decimal part to seconds
{{{ .893*60 = 54 }}}
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It will takes them 22 min 54 sec