First, deduct 15% from the total weight of 2400kg because that is water. That leaves you with 2040kg total weight. So the combined weight of cement, sand, and stone gives you 2040kg in a 1:2:5 ratio.
A 1:2:5 ratio is the equivalent of being out of parts of 8. So the amount of cement is 1 part out of 8 (1/8), sand is 2 out of 8 (2/8), and stone is 5 out of 8 (5/8).
Amount of cement is one-eighths of 2040kg so (1/8) * (2040) = 255kg Amount of sand is two-eighths of 2040kg so (2/8) * (2040) = 510kg Amount of stone is five-eighths of 2040kg so (5/8) * (2040) = 1275kg
