Question

7. Manoj and his younger sister Sandhya had their birthday yesterday i.e. Saturday, 15 th February, 2003. They were both born on Saturday. The sum of their ages is 23. Find their dates of birth. ​

Answer 1

The dates of birth of Manoj and Sandhya are February 15th, 1981 and February 15th, 1979 respectively.

Explanation:

Let's use a system of equations to solve the problem.

Let M be Manoj's age and S be Sandhya's age. We know that their ages sum up to 23, so:

M + S = 23

We also know that they were both born on a Saturday, which means their birthdays fall on the same day of the week. In 2003, February 15th was a Saturday, so we can assume that they were born on February 15th in different years. Let's represent the year of Manoj's birth as M_year and the year of Sandhya's birth as S_year.

Since they were both born on a Saturday, we know that the year of Manoj's birth plus his age (M_year + M) must have the same remainder when divided by 7 as the year of Sandhya's birth plus her age (S_year + S). In other words:

(M_year + M) mod 7 = (S_year + S) mod 7

We can simplify this equation by subtracting M from both sides and then substituting 23 - S for M:

(M_year + (23 - S)) mod 7 = (S_year + S) mod 7

Now we have two equations with two unknowns. We can solve for M_year and S_year by guessing values for S and then checking if there are integers M and S_year that satisfy both equations. We know that M and S must be positive integers and that their sum is 23. Here are a few guesses:

If S = 1, then M = 22 and the equation becomes:

(M_year + 22) mod 7 = (S_year + 1) mod 7

This simplifies to:

M_year mod 7 = (S_year + 6) mod 7

There are no integers M_year and S_year that satisfy this equation, since the two sides always have different remainders when divided by 7.

If S = 2, then M = 21 and the equation becomes:

(M_year + 21) mod 7 = (S_year + 2) mod 7

This simplifies to:

M_year mod 7 = (S_year + 5) mod 7

The only pair of integers that satisfies this equation is M_year = 2 and S_year = 4.

Therefore, Manoj was born on February 15th, 1981 and Sandhya was born on February 15th, 1979.

So the dates of birth of Manoj and Sandhya are February 15th, 1981 and February 15th, 1979 respectively.

Answer 2

to find the date of birth from the age, you need to subtract the number of years and days from the current date. In this case, the current date is 15 February 2003. The sum of their ages is 23, which means that Manoj and Sandhya have a difference of 23 years between their dates of birth. Since they were both born on Saturday, their dates of birth must be on the same day of the month. Therefore, we can assume that Manoj was born on 15 February 1980 and Sandhya was born on 15 February 2003. This is one possible solution, but there may be other solutions depending on the leap years and calendar changes.