The average of 20 numbers is 12. The average of the first 12 numbers is 11 and that of the next 7 numbers is 10. The last number is ?

Answer: Option B

Let the last number = x
According to the question,
⇒ 12 × 11 + 7 × 10 + x = 20 × 12
⇒ 132 + 70 + x = 240
⇒ x = 240 - 202
⇒ x = 38