A godown holds wheat and bajra in the ratio 7 : 3. After 60 quintals of the wheat is sold and none of the bajra is touched, the two stocks stand in the ratio 5 : 3. The bajra in the godown (in quintals) is:

Write the stocks as 7$k$ and 3$k$. Then $(7k-60)/3k=5/3$ → $21k-180=15k$ → $k=30$, so the bajra is $3\times 30=90$ quintals. (Check: wheat 210 falls to 150, and 150 : 90 = 5 : 3.) ₹210 and 150 quintals are the wheat before and after the sale, and 30 is only the value of $k$ — the bajra is the quantity that never moved, which is exactly why it can be found this way.