The mass ratio of cement, sand and stone for a concrete is 2:3:5. Now there are 12 tons of each of the three ingredients. If the sand is used up, how many tons of cement are left? How many tons of stones are missing?

The mass ratio of cement, sand and stone for a concrete is 2:3:5. Now there are 12 tons of each of the three ingredients. If the sand is used up, how many tons of cement are left? How many tons of stones are missing?

12 △ 3 = 4 (tons), cement: 4 × 2 = 8 (tons), 12-8 = 4 (tons); stone: 4 × 5 = 20 (tons), 20-12 = 8 (tons); answer: 4 tons of cement left, 8 tons of stone missing