If 378 Colns Consist Os One Rupee, 50 Paise and 25 Paise Whose Values Are Proportional To 13:11:7, The Number Of 50 Paise Coine Will Be

The key is that 13:11:7 is the ratio of the rupee value of each denomination, not the number of coins. Let the total values of the Re 1, 50 paise and 25 paise coins be 13k, 11k and 7k paise-equivalents.

Converting to coin counts: Re 1 coins = 13k/100, 50 paise coins = 11k/50 = 22k/100, 25 paise coins = 7k/25 = 28k/100. Total coins = 63k/100 = 378, so k = 600.

• Re 1 coins = 78
• 50 paise coins = 132
• 25 paise coins = 168

Check: 7800 : 6600 : 4200 = 13:11:7, and 78 + 132 + 168 = 378. For the other options, k would not be a whole number, so the Re 1 count would fail. Only 132 works for all three denominations.

This is a standard ratio-and-proportion question in the quantitative aptitude part of the General Studies paper. The same method, converting value ratios into unit counts, shows up in later CSAT and in data-based reasoning.

Trap: Applying 13:11:7 directly to the number of coins, which gives about 134 and tempts you to pick 133 or 136.