Numbers to 20 and Strategies: practice solutions, Grade 1 – download the PDF

1 Counting on from 6 ★★★

We start at 6 and count on: 7, 8, 9, 10, 11. That is five numbers.

Answer: you land on 11, so \(6 + 5 = 11\).

2 Ten and some ones ★★★

1. \(10 + 6 = 16\).
2. \(15 = 10 + 5\).
3. \(10 + 9 = 19\).
4. 12 is one ten and 2 ones.

Every teen number is a ten and some ones.

3 Missing numbers ★★★

1. 9, 10, 11, 12, 13, 14, 15.
2. 18, 19, 20, 21, 22, 23.

Each number is one more than the number before it, even after 20.

4 Easy doubles ★★★

1. \(3 + 3 = 6\)
2. \(4 + 4 = 8\)
3. \(6 + 6 = 12\)
4. \(7 + 7 = 14\)
5. \(9 + 9 = 18\)

A double means the same number added twice.

5 Counting back ★★★

1. 15: say 14, 13, 12. So \(15 - 3 = 12\).
2. 18: say 17, 16. So \(18 - 2 = 16\).
3. 12: say 11, 10, 9, 8. So \(12 - 4 = 8\).
4. 20: say 19. So \(20 - 1 = 19\).

6 Sticker collection ★★★

We add: \(9 + 4\). Start at 9 and count on 4: 10, 11, 12, 13.

Answer: Nina has 13 stickers.

7 Count the counters ★★★

The first frame is full: 10 counters. The second frame has 7 counters.

\(10 + 7 = 17\). There are 17 counters.

8 True or false? ★★★

1. True. Ten and five more is 15.
2. False. \(10 + 3 = 13\), and \(12 = 10 + 2\).
3. True. Taking the ten away from 16 leaves 6.

9 Make ten ★★★

1. 9 needs 1 to make ten. Split 4 into 1 and 3. \(9 + 1 = 10\), then \(10 + 3 = 13\). So \(9 + 4 = 13\).
2. 8 needs 2. Split 6 into 2 and 4. \(8 + 2 = 10\), then \(10 + 4 = 14\). So \(8 + 6 = 14\).
3. 7 needs 3. Split 5 into 3 and 2. \(7 + 3 = 10\), then \(10 + 2 = 12\). So \(7 + 5 = 12\).

10 Near doubles ★★★

1. \(6 + 6 = 12\), plus 1 is 13. So \(6 + 7 = 13\).
2. \(8 + 8 = 16\), plus 1 is 17. So \(8 + 9 = 17\).
3. \(5 + 5 = 10\), plus 1 is 11. So \(5 + 6 = 11\).
4. \(7 + 7 = 14\), plus 1 is 15. So \(7 + 8 = 15\).

11 Think addition ★★★

1. \(9 + 5 = 14\), so \(14 - 9 = 5\).
2. \(8 + 5 = 13\), so \(13 - 8 = 5\).
3. \(7 + 9 = 16\), so \(16 - 7 = 9\).
4. \(5 + 7 = 12\), so \(12 - 5 = 7\).

12 Fact family ★★★

The biggest number, 14, is the total.

\(6 + 8 = 14\) and \(8 + 6 = 14\).

\(14 - 6 = 8\) and \(14 - 8 = 6\).

13 Frog on the number line ★★★

Hop six times from 8: 9, 10, 11, 12, 13, 14.

The frog lands on 14, so \(8 + 6 = 14\).

14 Muffin trays ★★★

We add \(7 + 8\). We know \(7 + 7 = 14\), and 8 is one more than 7.

\(14 + 1 = 15\). The baker has 15 muffins.

15 Which is more? ★★★

\(8 + 5 = 13\) and \(7 + 7 = 14\).

14 is greater than 13, so \(7 + 7\) is the greater sum.

16 Find the missing number ★★★

1. From 7 to 10 is 3, from 10 to 15 is 5, so \(3 + 5 = 8\). \(7 + 8 = 15\).
2. \(13 - 6 = 7\). Check: \(7 + 6 = 13\).
3. \(18 - 9 = 9\), and \(9 + 9 = 18\) is a double.

The missing numbers are 8, 7 and 9.

17 Marbles in a bag ★★★

Step 1: he gives away 5, so \(18 - 5 = 13\). Count back: 17, 16, 15, 14, 13.

Step 2: he finds 3, so \(13 + 3 = 16\).

Answer: Omar has 16 marbles.

18 Find the mistake ★★★

Leo is not right. He used the double \(6 + 6 = 12\), but 7 is one more than 6.

He must add one more: \(12 + 1 = 13\). The correct answer is \(6 + 7 = 13\).

19 Three numbers to make ten ★★★

1. \(6 + 4 = 10\), then \(10 + 5 = 15\).
2. \(7 + 3 = 10\), then \(10 + 8 = 18\).
3. \(5 + 5 = 10\), then \(10 + 9 = 19\).

Totals: 15, 18 and 19.

20 Which ones make 16? ★★★

\(8 + 8 = 16\), yes. \(9 + 6 = 15\), no. \(10 + 6 = 16\), yes. \(20 - 4 = 16\), yes. \(18 - 3 = 15\), no. \(17 - 1 = 16\), yes.

The expressions equal to 16 are \(8 + 8\), \(10 + 6\), \(20 - 4\) and \(17 - 1\).

21 Two secret numbers ★★★

Think of a near double. Try \(6 + 7 = 13\). Seven is 1 more than 6, so it works.

The secret numbers are 6 and 7.

22 The school bus ★★★

First stop: \(12 - 5\). Think \(5 + 7 = 12\), so \(12 - 5 = 7\).

Next stop: \(7 + 6 = 13\). Check by making ten: \(7 + 3 + 3 = 13\).

Answer: there are 13 children on the bus.