why number 8549176320 is one of a kind?

A mathematics teacher took exams for his students. Out of the total students, 25% passed both the tests included in the exam. However, only 42% were able to clear the first test.

Can you find out the percentage of those students who passed the first test and also passed the second test?

What is a word made up of 4 letters, yet is also made up of 3. Sometimes is written with 9 letters, and then with 4. Rarely consists of 6, and never is written with 5.

Why do people go to bed?

There is a shop where written:
Buy 1 for $1
10 for $2
100 for $3
I needed 999 and still only paid $3. How could this be financially viable for the shop-keeper?

Can you guess the name of the month by looking the below rebus ?

What happened when the wheel was invented?

using four eights (8) and a one (1) and one mathematical symbol , create the number 100

A Man gave one of his sons 10 cents and another son was given 15 cents. What time is it?
Hint: Figure out the relation between time and number, is not so easy..:)

Name one eight-letter word with 'kst' in the middle, 'in' the beginning, 'and' at the end.?