Sean drank 3/5 of the water in his water bottle. He accidentally spilled 1/4 of the remaining water. As a result, he had 90 millilitres of water left in his water bottle. How much water did Sean have at first? Give your answer in millilitres
Let the total amount of water in bottle be x.
=> x - 3/5x - 1/4 (x - 3/5x) = 90 ml
=> ((5x - 3x)/5) - 1/4 ((5x - 3x)/5) = 90 ml
=> (2x/5) - 1/4 * (2x/5) = 90 ml
=> ((4 - 1) 2x)/(4 * 5) = 90 ml
=> (3 * 2x)/20 = 90 ml
=> 6x = 90 * 20 = 1800 ml
x = 1800/6 = 300 ml