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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 number is:

1. 19
2. 18
3. 20
4. 25

Correct answer: 25

Solution

Let the numbers be a, b, c, d. Then a+b+c = 54 and b+c+d = 48. Since d = 19, b+c = 29, so a = 54 - 29 = 25.

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