Question

Two years ago the mean age of 40 people was 11years.now a person left the group the mean age has changed to 12 years find the age of person who left the group

Answer 1

52 years.
two years ago the mean age for 40 ppl was 11 yrs. So total age two years ago should be 11 x 40 = 440 .

Now, after two years the total age should go up 2 times 40 people = 80 + 440 = 520.

When one person left, the for 39 ppl the mean age is 12. That is 12 times 39 = 468.

Deduct 520 - 468 = 52 years is the age of the person left.