Mr. ‘X’ has three children. The birthday of the first child falls on the 5th Monday of April, that of the second one falls on the 5th Thursday of November. On which day is the birthday of his third child, which falls on 20th December?

Correct Option (D)

The problem provides a reference point: 5th November is a Thursday.

To determine the day of the week for 20th December, the total number of days between 5th November and 20th December must be calculated:

• Number of days remaining in November from 5th November: 30 − 5 = 25 days.
• Number of days in December up to 20th December: 20 days.
• Total number of days = 25 (November) + 20 (December) = 45 days.

Next, the number of odd days is determined by dividing the total days by 7:

• Number of odd days = 45 ÷ 7 = 6 weeks and 3 odd days.

Since 5th November is a Thursday, the day for 20th December will be 3 days after Thursday:

• Thursday + 1 day = Friday
• Thursday + 2 days = Saturday
• Thursday + 3 days = Sunday

Therefore, 20th December is a Sunday.

Incorrect Options:

Options (A) Monday, (B) Thursday, and (C) Saturday are incorrect. The calculation based on the given reference point of 5th November being a Thursday leads to 20th December being a Sunday, not any of the other specified days.