Multiplication and division appear everywhere in real life. In 11 Plus Maths, these skills help students calculate patterns, ratios, and quantities efficiently and accurately.
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To multiply a number by 9: first multiply the number by 10, then subtract the original number from it:
212 × 9 = (212 x 10) - 212 = 2,120 - 212 = 1,908 |
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To divide a number by 5: first multiply by 2 and then move the digits to the right:
326 ÷ 5 = (326 × 2) ÷ 10 = 652 ÷ 10 . Move the d.p. 1 place to the left gives 65.2 |
To divide a number by 25: divide by 100, then multiply by 4:
475 ÷ 25 = (475 ÷ 100) x 4 = 4.75 x 4 = 19 |
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To multiply a number by 5: first divide by 2, then move the digits to the left:
2,343 × 5 = (2,343 ÷ 2) x 10 = 1,171.5 x 10. Move the d.p. 1 place to the right gives 11,715 |
To multiply a number by 25: multiply by 100, then divide by 4:
627 × 25 = (627 x 100) ÷ 4 = 62,700 ÷ 4 = 15,675 |
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To multiply a number by 12, first multiply the number by 10, then add twice the original number to it:
134 × 12 = (134 x 10) + (134 x 2) = 1,340 + 268 = 1,608 |
To divide a number by a multiple of 10 whose only non-zero digit is the leading digit 1: move the digits to the right by the same number of zeros that are in the multiple of 10, in this case 3 places as there are 3 zeros in 1,000
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To multiply a number by 101, first multiply by 100 then add the original number:
27 × 101 = (27 x 100) + 27 = 2,700 + 27 = 2,727 |
To multiply a number by 80, multiply the number by 2, then by 2 again, and again by 2, and finally by 10:
96 × 80 = (96 x 2 x 2 x 2) x 10 = (192 x 2 x 2) x 10 = (384 x 2) x 10 = 768 x 10 = 7,680 |
714 x 11 = (714 x 10) + 714 = 7,140 + 714 = 7,854