A can do a piece of work in 12 days and B in 15 days. They work together for 5 days and then B left. The days taken by A to finish the remaining work is
lcm of 12,15=60
lets assume total work to be 60 units
work per day for A = $$\frac{60}{12}$$ = 5 units
work per day for B = $$\frac{60}{15}$$ = 4 units
as they worked together for 5 days so total work completed = (5+4)*5 =45 days
now days taken by A to complete the left over work = $$\frac{60-45}{5}$$ = 3 days
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