Multiple choice

The average of 15 numbers is 40. The average of the first eight numbers is 30. If the average of the last eight numbers is 50, then the eighth number is

  1. $40$
  2. $45$
  3. $50$
  4. $35$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Sum of 15 numbers = 15 × 40 = 600. Sum of first 8 = 8 × 30 = 240. Sum of last 8 = 8 × 50 = 400. Note: 8th number is counted in both groups. Let 8th number = x. Then 240 + 400 - x = 600, so x = 640 - 600 = 40. The 8th number is 40. Option B (45) and C (50) are incorrect. Option D (35) is also wrong.

Keep practicing — related questions