12 girls have an average of 35 clips. When 3 more girls join in, the average number of clips for all the girls is 42. What is the average number of clips the new girls have?

clips

The total number of clips for 12 girls: 35 × 12 = 420

The total number of clips for (12 + 3) girls: 42 × (12 + 3) = 42 × 15 = 630

The difference: 630 – 420 = 210

Thus, the average for the new girls: 210 ÷ 3 = 70