Three years ago, the average age of A, B and C was 27 years. Five years ago the average age of B and C was 20 years. A's present age is _______.

Question: Three years ago, the average age of A, B and C was 27 years. Five years ago the average age of B and C was 20 years. A's present age is _______.

Solution:
ধরি, বর্তমানে A, B এবং C-এর বয়স যথাক্রমে a, b এবং c বছর।

তিন বছর আগে:
(a - 3 + b - 3 + c - 3)/3 = 27
⇒ (a + b + c - 9) = 81
⇒ a + b + c = 90 ............ (1)

পাঁচ বছর আগে:
(b - 5 + c - 5)/2 = 20
⇒ (b + c - 10) = 40
⇒ b + c = 50 ............ (2)

সমীকরণ (1) থেকে (2) বিয়োগ করলে:
(a + b + c) - (b + c) = 90 - 50
∴ a = 40

∴ A-এর বর্তমান বয়স 40 বছর।