Thursday, September 22, 2011

Impress your students with mental math tricks!

Squaring 2-digit numbers that end in 5

If a number ends in 5 then its square always ends in 25. To get the rest of the product take the left digit and multiply it by one more than itself.

35x35 ends in 25. We get the rest of the product by multiplying 3 by one more than 3. So, 3x4 = 12 and that's the rest of the product. Thus, 35x35 = 1225.

To calculate 95x95, notice that 9x10 = 90 and write down 9025 as the answer.

45x45: Calculate 4x5 = 20 and write down 2025.

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