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Week 8 Reflection

Exercise 1

What to do   

Use the information given to you to derive the answer to a similar problem.

1. If 9 × 20 = 180 what is 9 × 21  180
2. If 8 × 30 = 240 what is 8 × 31   248
3. If 4 × 40 = 160 what is 4 × 42   168
4. If 5 × 50 = 250 what is 5 × 51   255
5. If 3 × 60 = 180 what is 3 x 62   186
6. If 2 × 70 = 140 what is 2 × 73  146
7. If 4 × 80 = 320 what is 4 × 82  328

8)    If 2 × 90 = 180 what is 2 × 94  188

Exercise 2

What to do   

Use the information given to you to derive the answer to a similar problem.

1) If 9 × 20 = 180 what is 9 × 19  171

2) If 8 × 30 = 240 what is 8 × 29  232

3) If 7 × 40 = 280 what is 7 × 39  224

4) If 5 × 50 = 250 what is 5 × 49  245

5) If 3 × 60 = 180 what is 3 × 58  174

6) If 2 × 70 = 140 what is 2 × 67  134

7) If 4 × 80 = 320 what is 4 × 78   312

8) If 2 × 90 = 180 what is 2 × 86 1 72

Exercise 3

What to do   

Use the information given to you to derive the answer to a similar problem.

1. If 9 × 20 = 180 what is 9 × 22  198
2. If 7 × 30 = 210 what is 7 × 32  224
3. If 5 × 40 = 200 what is 5 × 43  215
4. If 4 × 50 = 200 what is 4 × 51  204
5. If 3 × 60 = 180 what is 3 × 61  183
6. If 6 × 70 = 420 what is 6 × 73  438
7. If 6 × 80 = 480 what is 6 × 81  186

8)    If 8 × 90 = 720 what is 8 × 92  736

Exercise 4

What to do   

Use the information given to you to derive the answer to a similar problem.

1. If 9 × 20 = 180 what is 9 × 18  162
2. If 7 × 40 = 280 what is 7 × 37  259
3. If 5 × 40 = 200 what is 5 × 38  190
4. If 4 × 50 = 200 what is 4 × 47  188
5. If 3 × 60 = 180 what is 3 × 56  171
6. If 6 × 70 = 420 what is 6 × 67  402
7. If 6 × 80 = 480 what is 6 × 78  468

8)    If 8 × 90 = 720 what is 8 × 88  704

Exercise 5

What to do   

Use the information given to you to derive the answer to a similar problem.

1. If 4 × 200 = 800 what is 4 × 201  804
2. If 7 × 300 = 2100 what is 7 × 301  2017
3. If 8 × 400 = 3200 what is 8 × 402  3216
4. If 9 × 500 = 4500 what is 9 × 501  4509
5. If 5 × 600 = 3000 what is 5 × 602  3010
6. If 3 × 700 = 2100 what is 3 × 704  2112
7. If 2 × 800 = 1600 what is 2 × 803  1606

8) If 6 × 900 = 5400 what is 6 × 903  5418

Exercise 6

What to do   

Use the information given to you to derive the answer to a similar problem.

1. If 4 × 200 = 800 what is 4 × 199 ?
2. If 7 × 300 = 2100 what is 7 × 299 ?
3. If 8 × 400 = 3200 what is 8 × 398 ?
4. If 9 × 500 = 4500 what is 9 × 498 ?
5. If 5 × 600 = 3000 what is 5 × 597 ?
6. If 3 × 700 = 2100 what is 3 × 698 ?
7. If 2 × 800 = 1600 what is 2 x 797 ?
8. If 6 × 900 = 5400 what is 6 × 897 ?

Exercise 7

What to do   

Use the information given to you to derive the answer to a similar problem.

1. If 2 × 25 = 50 what is 2 × 24   48
2. If 4 × 25 = 100 what is 4 × 27   92
3. If 3 × 15 = 45 what is 3 × 14   42
4. If 4 × 15 = 60 what is 4 × 17   68
5. If 6 × 15 = 90 what is 6 × 14   84
6. If 2 × 25 = 50 what is 2 × 26   52
7. If 4 × 25 = 100 what is 4 × 24   96
8. If 3 × 15 = 45 what is 3 × 16   48
9. If 4 × 15 = 60 what is 4 × 13   52
10. If 6 × 15 = 90 what is 6 × 17   102

Exercise 8

What to do   

Use the strategy add a little/subtract a little to solve these problems.  

Julie wanted to find 3 × 28.

She knows that 28 is near 30, so she used 3 × 30 = 90 and subtracted 3 × 2 = 6 to get the answer.  

Julie recorded this in her maths book

3 × 28 = 90 – 6 = 84

Using Julie’s method find the answer to the following problems.  Record your working like Julie did.

1) 4 × 19       76       (2) 3 × 41 121 (3) 5 × 59  295

4) 7 × 52 364          (5) 4 × 73 292 (6) 3 × 37  111

7) 6 × 102  612 (8) 5 × 301 1502  (9) 4 × 698  2792

10) 3 × 499  1497 (11) 7 × 602 4214 (12) 9 × 3999  35,991