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?

A man dies of old age on his 25 birthday. How is this possible?

A certain street contains 100 buildings. They are numbered from 1 to 100. How many 9's are used in these numbers?

What number when divided in half becomes zero?

Two guards were on duty outside a barracks. One faced up the road to watch for anyone approaching from the North. The other looked down the road to see if anyone approached from the South. Suddenly one of them said to the other, "Why are you smiling?"

How did he know his companion was smiling?

Below is the sum of symbols in each row and column in the figure. Analyzing the figure, can you find out the value of the symbols?

Place a mathematical symbol between the numerals 5 and 9 in such a way that the resulting number is greater than 5 but smaller than 9.

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

What has 88 keys?

Which tank will fill first?