Working together, merry and pippin can build a wall in 4.5 hours. if merry can do the job alone in 6 hours working alone, how long would it take pippin to build the wall when working alone?

ANSWER


EXPLANATION

If Merry and Pippin can build a wall in 4.5 hours, their working rate is



If Merry can do the work alone in 6 hours, then her rate of working is,



If Pippin takes

to do the work alone, then her working rate is



If we add their individual rates it should give us their combined rate.

This means that,



or



This implies that,



We collect LCM on the right hand side to get,



This simplifies to,



We cross multiply to get,



Or



Therefore it would take Pippin, 18 hours to build the wall when working alone.