SSC MTS 5 Aug 2019 Shift 1 Paper

Average age of 12 boys is = 15
Sum of ages of 12 boys = 15 × 12 = 180
Average age of 18 girls = 13
Sum of ages of 18 girls = 12 × 18 = 216
Sum of age 12 boys and 18 girls = 180 + 216 = 396
Average age of 12 boys and 18 girls = 396/(12 + 18) = 398/30 = 13.2