What’s the difference between disk method, washer method and shell method in calculus?

They are names for three ways of handling one number.

Disk method: Add the numbers in a circle and then cover them up with the same number, so that you have a single “disc” to work on when you’re adding. For example, the answer to *1+2* would be 3 since its top number is covered by a *3*.

Holes-in-the-sides method: Put all of your numbers into two rows, eight per row. The left column will be labeled with letters from A through H (representing 1 though 8) and the right column will be labeled with numbers from 9 through 1 (9 being 8 plus an additional carries digit). Now fill in digits in each row. The largest multiple of nine which has not been filled in is the answer to the problem.