Multiple choice

Out of four numbers the average of the first three is 18 and that of the last three is 16. If the last number is 19, the first is -

  1. $19$
  2. $18$
  3. $20$
  4. $25$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Let four numbers be a,b,c,d. Given: (a+b+c)/3 = 18 → a+b+c = 54. Also: (b+c+d)/3 = 16 → b+c+d = 48. Subtracting: (a+b+c) - (b+c+d) = a-d = 54-48 = 6 → a = d+6. Given d = 19, so a = 19+6 = 25.

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