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------------------------------------------------ Out of four numbers, the average of the first three is 16, and the average of the last three is 15. If the last number is 20, what is the first number?

Answer :

Final answer:

The first number in a series of four consecutive numbers with specific average conditions is 3.

Explanation:

The question gives us two average scenarios. First, the average of the first three numbers is 16. This means the sum of those three numbers is 3 * 16 = 48. Second, the average of the last three numbers is 15. This indicates that the sum of those three numbers is 3 * 15 = 45.

The numbers being referred are consecutive, which means the second and third numbers are included in both the sums. Hence we have the first number + second number + third number = 48 and second number + third number + fourth number (which is 20 as given in the question) = 45.

To find the first number, subtract 45 (the sum of the last three numbers, from the first equation) from 48 (the sum of first three numbers):

48 - 45 = 3. So, the first number is 3.

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