BY ONE MORE THAN THE ONE BEFORE
This special type of multiplication is for multiplying numbers whose first figures are the same
and whose last figures add up to 10, 100 etc.
For example, 52 × 58, where both numbers start with 5 and 2 + 8 = 10.
Suppose we want to find 43 × 47 in which both numbers begin with 4 and the last figures (3 and 7) add up to 10. Multiply 4 by the number One More: 4 × 5 = 20. Then simply multiply the last figures together: 3 × 7 = 21. So 43 × 47 = 2021 where 20 = 4×5, 21 = 3×7. Similarly 62 × 68 = 4216 where 42 = 6×7, 16 = 2×8. 7 8 9 Find 204 × 206. Here both numbers start with 20, and 4 + 6 = 10, so the method applies. 204 × 206 = 42024 (420 = 20×21, 24 = 4×6).
Practice A Multiply the following:
a 73 × 77 b 58 × 52 c 81 × 89 d 104 × 106 e 42 × 48 f 34 × 36 g 93 × 97 h 27 × 23 i 297 × 293 j 303 × 307
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