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

A girl has as many brothers as sisters, but each brother has only half as many brothers as sisters. How many brothers and sisters are there in the family?

What will be the best approach to finding all the prime numbers less than 75 that leave an odd reminder when we divide them with 5?

An express train takes 3 seconds to enter the tunnel which is 1 km long.
If it is travelling at 120 km an hour, how long will it take to pass completely through the tunnel?

Can you arrange four 9's and use at most 2 math symbols, to make the total 100?

What does this mathematical rebus means ?

Can you write down eight eights so that they add up to one thousand?

We know that the number 7 is the prime followed by a cube. Which next number is also a prime followed by a cube?

Find out the missing number in the picture attached:

Before the start of the car race, John and Jacob have the same amount of fuel in their car. With this fuel, John can drive for 4 hours while Jacob can drive five hours.
After a time they realize that the amount of fuel left in John's car is 1/4th of the fuel in Jacob's.

For how long they are racing?