Question 1084940
two identical tap fill 2/5 of a tank in 20 mins, which means,
one tap fill 1/5 of a tank in 20 mins
and there is still 3/5 of a tank waiting to be filled, 
so it takes three times 20 mins to fill the remaining tank.
3 * 20 = 60 mins

i would love to hear more alternative ways to solve the problems.
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