Q. The average of 30 numbers is 12. The average of the first 20 of them is 11 and that of the next 9 is 10. The last number is
✅ Correct Answer: (D)
50
Explanation: Given , Sum of 30 numbers = 30 × 12 = 360
Sum of the first 20 numbers = 20 × 11 = 220
and Sum of the next 9 numbers = 9 × 10 = 90
∴ Last number = Sum of 30 numbers – Sum of the first 20 numbers – Sum of the next 9 numbers
Last number = 360 – 220 – 90
Last number = 360 – 310 = 50
Explanation by: Parvesh Kanani
Given , Sum of 30 numbers = 30 × 12 = 360
Sum of the first 20 numbers = 20 × 11 = 220
and Sum of the next 9 numbers = 9 × 10 = 90
∴ Last number = Sum of 30 numbers – Sum of the first 20 numbers – Sum of the next 9 numbers
Last number = 360 – 220 – 90
Last number = 360 – 310 = 50
Sum of the first 20 numbers = 20 × 11 = 220
and Sum of the next 9 numbers = 9 × 10 = 90
∴ Last number = Sum of 30 numbers – Sum of the first 20 numbers – Sum of the next 9 numbers
Last number = 360 – 220 – 90
Last number = 360 – 310 = 50