Discussion

Explanation:

Five years ago the average age of husband and wife was 23 years. Today the average age of husband, wife and child is 20 yrs. How  old is child?

Five years ago average of husband and wife = 23 years
Present average of husband and wife = 23 + 5 = 28 years

Present sum of the ages of husband and wife = 28 × 2 = 56.
Present sum of the ages of all 3 members = 20 × 3 = 60.

∴ Present age of the child = 60 - 56 = 4 years.

Hence, option (b).

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