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Answers for Mental multiplication worksheet

It is important to note that these suggested answers are just one of the many possible strategies that children may use.

1.	439 x 10 Possible strategy: front end multiplication 10 x 400 = 4 000 10 x 30 = 300 10 x 9 = 90 Therefore: 429 x 10 = 4 000 x 300 x 90 = 4 390
2.	2 x 18 x 5 = 180 Possible strategy: multiplication in stages using base ten 2 x 18 x 5 = 10 x 18 = 180
3.	4 x 36 x 5 Possible strategy: using the known facts of the previous question. 4 x 36 x 5 = 4 x previous algorithm = 4 x 2 x 18 x 5 = 4 x 180 = 720
4.	102 x 21 = 2142 Possible strategy: multiplication in stages 102 x 21 = (100 x 21) + (21 x 2) = 2 100 + 42 = 2 142

5.	999 x 6 = 5994 Possible strategy: rounding 999 is very close to 1 000. Therefore since 1 000 x 6 = 6 000, 999 x 6 = 6 000 - 6
6.	25 x 8 = 200 Possible strategy: Doubling a known fact 25 x 8 = 25 x 4 x 2 = 100 x 2 = 200
7.	25 x 9 Possible strategy: use the previous solution 25 x 9 = 25 x 8 + 25 = 200 + 25 = 225
8.	32 x 50 = 1600 Possible strategy: Halving and doubling 32 x 50 = 16 x 100 = 1 600
9.	32 x 52 = 1664 Possible strategy: Using previous question 32 x 52 = 16 x 100 + 2 x 32 = 1 600 + 64 = 1 664

10.	75 x 6 = 450 Possible strategy: multiplication in stages using a known fact 75 x 6 = 3 x 25 x 6 = 3 x 150 = 450
11.	8 x 17 = 136 Possible strategy: repeated doubling 8 x 17 = 2 x 2 x 2 x 17 = 136
12.	13 x 12 = 156 Possible strategy: using table knowledge 13 x 12 = 12 x 12 + 12 = 139
13.	24 x 125 = 3000 Possible strategy: using the known fact provided 24 x 125 = 3 x 8 x 125 = 3 x 1 000 = 3 000
14.	26 x 7 x 33 = 6006 Possible strategy: using the known fact provided 26 x 7 x 33 = 2 x 13 x 7 x 11 x 3 = 6 x 1 001 = 6 006

15.	900 ÷ 225 Possible strategy: using the known fact provided Since 30 x 30 = 900 And 30 can be expressed as 2 x 15 Then 30 x 30 = 2 x 15 x 2 x 15 = 900 Then 4 x 225 = 900 Therefore there are four 225s in 900.
16.	2^¹²= 4096 Possible strategy: doubling Since 2¹⁰ = 1024 2¹²= 1024 x 2 x 2 = 4096

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