Quick way to add 30 percent?

Answer 1

The simplest, one-step, way is to multiply by 1.3.

But if your arithmetical skills are not up to that the longer way is:

Step 1: divide the number by 10 (move the decial point one place to the left)

Step 2: multiply the result by 3

Step 3: add this to the original number.

Or

Step 1: divide the number by 10 (move the decial point one place to the left)

Step 2a: add this to the original number (+ 10%)

Step 2b: add again (+ 20%)

Step 2c: add yet again (and you've got + 30%).