Maths Quiz - Multiplication and Division 2 (Medium) (Answers)
This is the second of our medium level Eleven Plus maths quizzes on multiplication and division. In the first, we learned some handy techniques for multiplying and dividing which, if you remember them, will improve your mental arithmetic considerably. The best way to remember something of course, is to practice!
Here are some tips which may help you:
There are many more useful strategies you can use – you may even have some of your own. Whatever method you choose, as long as you reach the correct answer quickly, then it’s fine. Now try these teasers and see how you fare. Good luck!
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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