How many words can a pen with half refill write?

You have two strings whose only known property is that when you light one end of either string it takes exactly one hour to burn. The rate at which the strings will burn is completely random and each string is different.

How do you measure 45 minutes?

There is an English word that can be used up to four times in a row without modifying the spelling and form a valid grammatical sentence.

Do you know what word is that?

In a school, there are four subjects. Seventy percent of students study English, seventy five percent of students study Science, eighty five percent of students study Mathematics and eighty percent of students study Spanish.

Can you calculate the percentage of students that study all four subjects?

If,

6 / 7 = 2
3 / 9 = 7
8 / 2 = 6

Then

4 / 5 = ?

I have an eye but still cannot see.

Who am I?

What month of the year has 28 days?

Solve the rebus below.

Place the numbers from 1 to 9 in the circles in a manner that each side of the triangle sums up to 17.

I have branches, but no fruit, trunk or leaves. What am I?