If 21x = 79x, what is the value of x?

In a basket of apples,
when counted in twos, there was one extra
when counted in threes, there were two extra when counted in fours, there were three extra
when counted in fives, there were four extra
when counted in sixes, there was five extra.

However, if the apples were counted in sevens, no extra apple was left. Can you calculate the minimum number of apples that were present in the basket?

Double it and multiply it by 4. Then divide it by 8 and you’ll have it once more. What number is it?

Baseball bat and ball cost $100. If the bat cost $99 more than the ball, what is the cost of each?

A girl is twice as old as her brother and half as old as her father. In 50 years, her brother will be half as old as his father. How old is the daughter now?

Look at this sequence from top to bottom. What is the next number in the sequence?
1
11
21
1211
111221
312211

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?

'S' refers to the number of seconds in a day and 'H' refers to the number of hours in ten years. Which quantity out of these two is greater?

Arrange the numbers 1, 2, 3, 4, 5, 6, 7, 8 and 9 above and below the division line in a manner that the thus formed fractions equal to 1/3.

(You can use one number only once)

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