Question

Alvin and Geraldine are addressing invitations to their wedding. Alvin can address one every
thirty seconds and Geraldine can do one in 40 seconds. How long will it take them to
address 140 invitations?

Answer 1

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%2F13+%2B+1%2F40+=+140%2Ft+

Multiply both sides by +13%2A40%2At+

+40t+%2B+13t+=+13%2A40%2A140+

+53t+=+72800+

+t+=+1373.58+ sec

Convert this to minutes

+1373.58+%2F+60+=+22.893+ min

Convert the decimal part to seconds

+.893%2A60+=+54+

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It will takes them 22 min 54 sec