Squaring Numbers From 80 To 100

In the previous post, we have learned how to square 2-digit numbers mentally. In this post, we learn specifically another strategy on how to square numbers from 80 to 100.

Steps in Squaring Numbers From 80 to 100

Step 1: Subtract the number from 100.

Step 2: Square the difference.

Step 3: Subtract the result in 1 from the given number.

Step 4: If the result is a 2-digit number, append the result in 3 to the result in 2 (see Examples 1 and 2). If the result is a 3-digit number, add the hundreds digit to the ones digit of the given number and then append the 2 digits (see Example 3).

Example 1: 942

Step 1: We subtract 94 from 100. That is, 100 – 94 = 6.

Step 2: Square 6 which equals 36. 

Step 3: 94 – 6 = 88

Step 4: Append 88 and 36.

So, 942 = 8836.

Example 2: 952

Step 1: We subtract 95 from 100. That is, 100 – 95 = 5.

Step 2: Square 5 which equals 25.

Step 3: 95 – 5 = 90

Step 4: Append 90 and 25.

So, 952 = 9025

Example 3: 882

Step 1: We subtract 88 from 100. That is, 100 – 88 = 12.

Step 2: Square 12 which equals 144.

Step 3: 88 – 12 = 76

Step 4: We should append 76 and 144 but it is a 3-digit number, so we add the hundreds digit of the result in 2 (that is the 1 in 144) to the ones digit of the result in Step 3 (the 6 in 76) and append the remaining 2-digit number. This results to 7744.

So, 882 = 7744

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  1. Pingback: Math Shortcut: Squaring Numbers from 50 to 70

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