I can always remember exponent rules by recalling what exponents mean and by expanding the expression, which means writing it the long way. 23 means 2 × 2 × 2 and 25 means 2 × 2 × 2 × 2 × 2. Then 23 x 25 means (2 × 2 × 2) × (2 × 2 × 2 × 2 × 2). I count that 2 is multiplied 8 times, so I can write that as 28. Notice that 3 + 5 = 8, so the rule for multiplying powers with the same base must be that I add together the exponents! I can use my calculator to find out that 28 = 256.