a fill pipe can fill 2 / 5 of cistern in 30 minutes in how many minutes , it can fill 4 / 5 of the cistern ?
"2 / 5 of the cistern can fill in 30 min 4 / 5 of the cistern can fill in = 30 * 5 / 2 * 4 / 5 = 60 min answer is e"
divide(30, 2)