Multiplying and dividing by two digits; divisibility · Usually met around P4
Squares to 25
Ends in 5: tens × next number, then 25.
How to do it
Method
Ends in 5: tens × next number, then 25
25²: 2 × 3 = 6 → 625
Another way
Column multiplication
25² = 25 × 25 = 625
In full
Learn 1² to 25² by heart. Lots of later tricks use them. Squares ending in 5 are the easiest: 25² → 2 times the next number, 3: 2×3=6, then stick 25 on the end → 625. 35² → 3×4=12 → 1225. You can also multiply in columns: 25² is 25 × 25, which also gives 625.
Worked examples
Have a go first, then open each one for the answer and the working.
Example 1
20²
Show the answer and working
Answer: 20² = 400
20² is 20 × 20 = 400
Example 2
7²
Show the answer and working
Answer: 7² = 49
7² is 7 × 7: ×7 is ×5 and ×2, 7 × 5 = 35, 7 × 2 = 14, 35 + 14 = 49
Example 3
21²
Show the answer and working
Answer: 21² = 441
21² is 21 × 21: split 21 into 20 and 1, 20 × 21 = 420, 1 × 21 = 21, 420 + 21 = 441
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