Multiple choice

The average of 9 numbers is 40. If the average of the first five numbers is 38 and that of the last five is 50, then what is the fifth number?

  1. 90

  2. 84

  3. 78

  4. 80
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Sum of 9 numbers = 9 × 40 = 360. Sum of first 5 = 5 × 38 = 190. Sum of last 5 = 5 × 50 = 250. The 5th number is counted in both sums, so: 190 + 250 - 5th number = 360. Therefore, 5th number = 190 + 250 - 360 = 80.

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