How many words can a pen with half refill write?

When I get multiplied by any number, the sum of the figures in the product is always me. What am I?

What does the below image rebus riddle means ?

Prove that twice of ten is the same as twice of eleven.

You have a three-gallon and a five-gallon measuring device. You wish to measure out four gallons.

There is a square piece of paper with a hole that is denoted by the circle on the top right side in the given picture. You have to cut the paper in a manner that it forms two and only two separate pieces of paper and then rearrange the pieces in a manner that the holes come in the centre of the paper.

Without looking at a calendar, within a minute name, a boy's name using 5 consecutive 1st letters of 5 consecutive months

I travel all around the world but always stay in the corner. What am I?

I’m tall when I’m young, and I’m short when I’m old. What am I?

What English word has three consecutive double letters?