A can do a work in 72 days and B in 90 days. If they work on it together for 10 days, then what fraction of work is left?
In 10 days ,they together will do =Â $$10\left(\frac{1}{90}+\frac{1}{72}\right)=10\left(\frac{4+5}{360}\right)=\frac{1}{4}\ part\ of\ work\ .$$
So, work left =Â $$\left(1-\frac{1}{4}\right)=\frac{3}{4}\ .$$
A is correct choice.
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