the mean of five numbers is 60 out of which the mean of four numbers is 50 . find the 5th number
Answers
The average of 9 numbers is 40
We know Average = Sum of numbers/no. of numbers
Sum of numbers = average of numbers × no. of numbers
Sum of numbers = 40 × 9 = 360
The average of first five numbers is 38
The sum of first five numbers
38 × 5 = 190
Sum of the last five numbers is 50
50 × 5 = 250
Sum of first five and last five numbers
190 + 250 = 440
In the sum of first five and last five numbers the fifth number is common in above total
The fifth numbet is 440 - 360 = 80
Therefore 5th number is 80
Answer the fifth number is 80
To check the correctness of answer from the sum of first five numbers, 80 is substracted, similarly from last five numbers, also 80 is substracted. The sum of first four numbers, last four numbers and 5th number 80 should be 360. Accordingly
First four numbers 190 - 80 = 110
Last four numbers 250 - 80 = 170
Sum of all 9 numbers = 110 + 80 + 170 = 360
Means answer 80 is correct.