Multiple choice

Out of the four numbers, the average of the first three is 16 and that of the last three is 15. If the last number is 20, then the first number is

  1. 28

  2. 23

  3. 21

  4. 38
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let four numbers be a, b, c, d. Given: (a+b+c)/3 = 16, so a+b+c = 48. Also: (b+c+d)/3 = 15, so b+c+d = 45. Given d = 20, then b+c = 25. Substituting in a+b+c = 48: a + 25 = 48, so a = 23. The first number is 23, which matches Option B.

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