Mohan was married 5 years ago. At present his age is six fifth of his age at the time of marriage. His wife is 3 years younger than Mohan. What is his wife's present age?

Introduction / Context:
Here we are given a relationship between Mohan's age now and his age at the time of marriage, along with the fact that his wife is 3 years younger than him. Using these details, we convert the verbal description into equations and determine first Mohan's current age and then his wife's age.

Given Data / Assumptions:

• Mohan was married 5 years ago.
• His present age is 6/5 times his age at the time of marriage.
• His wife is 3 years younger than Mohan at present.
• We must find his wife's present age.

Concept / Approach:
Let M be Mohan's present age. Since he married 5 years ago, his age at that time was M - 5. The relation says M = (6/5) * (M - 5). We solve this linear equation to get M. Then subtract 3 to obtain his wife's current age. This is a straightforward proportional age problem.

Step-by-Step Solution:
Let Mohan's present age be M years. Five years ago, at the time of marriage, his age was M - 5 years. Given that M = (6/5) * (M - 5). Multiply both sides by 5 to remove the denominator: 5M = 6(M - 5). So 5M = 6M - 30. Rearrange to get -M = -30, so M = 30 years. His wife is 3 years younger, so wife's present age = 30 - 3 = 27 years.

Verification / Alternative check:
At the time of marriage, Mohan was 30 - 5 = 25 years old. According to the given relation, his present age should be 6/5 of 25, which equals 30. This matches our computed value. His wife, at 27 years, is indeed 3 years younger than him, so all conditions are satisfied.

Why Other Options Are Wrong:
If his wife were 21 or 24 years old, Mohan's age would not match the derived 30 years under the 6/5 relation. An age of 30 years for the wife would make her the same age as Mohan, contradicting the statement that she is younger. The value 25 years also fails the condition of being exactly 3 years younger than Mohan at 30 years. The only consistent option is 27 years.

Common Pitfalls:
A common mistake is to take 6/5 of the present age instead of the marriage age, or to add 5 instead of subtracting 5 when finding the marriage age. Some learners also forget to toggle the equation correctly and miscalculate the linear step. Clearly identifying which age corresponds to which time helps prevent errors.

Final Answer:
Thus, Mohan's wife is presently 27 years old.