Can you find out which number multiplied by itself will give the output as 12345678987654321?

A famous swimmer can swim downstream in a lake in exactly 40 minutes with the lake current.
He can swim upstream in that lake in exactly 60 minutes against the lake current.
The length of the lake is 2 km.

How long he can cover the distance of one side at a still lake with no current?

Find the value of "?" in the ball picture Riddle below:

John can eat 27 chocolates in an hour, Jacob can eat 2 chocolates in 10 minutes, and Jolly can eat 7 chocolates in 20 minutes. How long will it take them to share and eat a box of 120 chocolates whilst playing Chess?

John drives to his office at 20km/hr. After reaching the office, he realizes that today is a holiday. He went back at an average speed of 30km/hr. Discounting the time spent in the stoppage what was the average speed of his journey?

I throw two dice simultaneously.

What is the probability of getting a sum as 9 of the two numbers shown?

Use the numbers 2, 3, 4 and 5 and the symbols + and = to make a true equation. Conditions: Each must be used exactly once and no other numbers or symbols can be used.

How do you go from 98 to 720 using just one letter?

Can you find out the remainder when 3^300 is divided by 5?

Can you think of a smallest +ve number such that if we shuffle the digits of the number, the new number becomes double the original number?