What has many keys but can’t open a single lock?

In the image given, you can find several triangles. Can you count them all?

A Doctor always sneezes before the rain. Doctor sneezes, Will it rain?

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?

The dirtier I get, the whiter I look. Who am I?

Decode the movie name from the below picture?

A man has to get a fox, a chicken, and a sack of corn across a river.

He has a rowboat, and it can only carry him and one other thing.
If the fox and the chicken are left together, the fox will eat the chicken.
If the chicken and the corn are left together, the chicken will eat the corn.

How does the man do it?

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?

After teaching his class all about Roman numerals (X = 10, IX=9 and so on) the teacher asked his class to draw a single continuous line and turn IX into 6. The teacher's only stipulation was that the pen could not be lifted from the paper until the line was complete.

The square root of number 121 is "11". What is the square root of the number "12345678987654321."?