Yes, you need copper ore:iron ore in the ratio 3:5. Total 8 tons of the mix in this ratio will give 1 ton of alloy A.

If you have 60 tons of copper ore, it is enough for 60/3 = 20 tons of alloy A.

If you have 90 tons of iron ore, it is enough for 90/5 = 18 tons of alloy A.

Since iron ore is available for only 18 tons of alloy A, you can make only 18 tons of alloy A.

The leftover copper ore alone cannot make any alloy A and hence will be leftover only.

Answer must be 18.

(A)

Note: This reminds me of our maximum power of 6 in 40! kind of questions. We have many 2s but fewer 3s. We can make only as many 6s as the number of 3s we have. The leftover 2s alone cannot make a 6. Makes sense?

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Karishma

Veritas Prep GMAT Instructor

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