The average of 40 numbers is 36. The average of the first 25 numbers is 31 and the average of the last 16 numbers is 43. Find the 25th number.
Show answer & explanation
Correct answer: B
Explanation
The correct answer is option 2 i.e 23
| Understanding | Application |
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We will use the formula of average to find the correct answer. Average = sum of observation/number of observations Which can be written as Sum of observation = average × number of observations |
The sum of the first 40 numbers = 40 × 36 ⇒ 1440 The sum of the first 25 numbers (1st to 25th) = 25 × 31 ⇒ 775 The sum of the last 16 numbers (25th to 40th) = 16 × 43 ⇒ 688 25th number = sum of first 25 numbers + sum of last 16 numbers - the sum of all numbers ⇒ 25th number = 775 + 688 - 1440 ⇒ 1463 - 1440 ⇒ 23 |