Question

The mean of 9 numbers is 50. If one number is included, their mean becomes 55. Find the included number.

Answer 1

Mean = Sum of all observations/total no. of observations
50=sum of all observations/9
Sum of all observations=450
If one number is added, mean = 55
Now, total no. of observations = 9+1=10
Let the included number be x.
Therefore, 55=Sum of all earlier observations + x/10
55=450+x/10
550=450+x
x=550-450
x=100

Answer 2

According to me this could be the answer .
Hope it will never let you down