I can solve the following problems in particular:

AUDIO MEMORY

Ability to repeat a 100-digit random number given by the audience, after hearing it only once, in both forward and reverse orders.

ROOTS

1. Square root of a number upto 1 Million
2. Cube root of a number upto 100 Million
3. Fourth root of a number upto Million
4. Fifth root of a number upto 10 Billion
5. Sixth root of a number upto 1 Trillion

MULTIPLICATION

Ability to multiply a maximum of five-digit number with another five-digit number in about 25 seconds using a pen and paper.

CALENDAR (AD or BC Infinite Years)

* If date, month and year are given, can tell the day of the week within a second.
* If the day, month and year are given, he can tell the day.
* And if the day, date and year are given, can tell the month.