If Rahul celebrated his birthday on Saturday in 1989. When will he celebrate his next birthday on same day?

1995

Divide last 2 digit of year by 4 and if Remainder is :

1  →   Calendar will repeat after 6 years

2  →   Calendar will repeat after 11 years

3  →   Calendar will repeat after 11 years

0  →   Calendar will repeat after 28 years

1989   divide 89 by 4  =  89/4  =  Remainder 1

Remainder is 1, so calendar repeat after 6 years i.e. 1995 .