A box has 210 coins of denominations one-rupee and fifty paise only. The ratio of their respective values is 13 : 11. The number of one-rupee coin is

Answer: Option D

Respective ratio of the NUMBER of coins;
= 13 : 11 × 2 = 13 : 22
Hence, Number of 1 rupee coins;
= $$\frac{13\times 210}{13+22}$$   = 78