🎂 Ages & Error Correction
2 exam question types, fully solvedTwo close cousins live here. Age problems add the idea of time passing; error-correction problems fix a value that was written down wrong. Both still run on total average count.
Ages — the time shortcut. If nobody joins or leaves, every member ages by the same amount, so the average just slides with the clock:
No totals needed — a family of 6 averaging 20 today averaged five years ago. When someone joins, leaves, or is born, fall back on totals; remember a newborn's age is 0, and any leftover years are the time that passed for the others.
Error correction — fix the sum. The count never changes; only the total was wrong. Repair it and re-divide:
Direction first: if the correct value is bigger than the wrong one the average rises, otherwise it falls. An interchange of two values changes the sum by (right value − used value). “84 instead of 48” means 48 is the correct one.
4 children average 10; adding the mother makes it 13. Mother .
Q1The average age of 5 students and their teacher is 20. Without the teacher it is 18. The teacher's age is:
Q2The average age of a family of 6 is 25 now. Five years ago the average age was:
Q3The average of 8 numbers is 25. One number, 46, was read as 64. The correct average is:
Real exam questions — Ages & Error Correction
2 question types · 8 solved examples from real SSC papersAges shift one-for-one with time when the group size holds; misread-value questions change only the sum, never the count.
If the group stays the same size, EVERY member ages equally: years later the average is simply (current average ); years ago it is (current average ). No need to touch the totals.
Join / leave / born: build totals on the correct counts and subtract. A newborn's age is 0 — if the maths leaves a remainder, it is the time that passed for the others, not the baby's age.
The average age of 4 children is 10. If the mother's age is included, the average becomes 13. Find the mother's age.
The average age of a family of 6 is 22. If the grandfather, aged 72, is excluded, find the new average.
The average age of 6 family members is 20 years now. What was the average 5 years ago?
The average age of the boys in a class was 16. When 4 boys (average age 13) were admitted, the average dropped by 0.5. Find the original number of boys.