How can i easily memorize pi without pencil and paper

Anew shopping mall is gaining in popularity. every day since it opened, the number of shoppers is 5% more than the number of shoppers the day before. the total number of shoppers over the first 10 days is 1258 how many shoppers were on the first day?

Suppose you have 10 skittles. 5 green and 5 red. you choose 4 without looking. what is the probability that all 4 skittles will be green?

Build is 120 wide 20 feet high 48 feet long how many cubic feet and the volume