Multiplying and dividing negative numbers
The Maths Habit
Kai faces the board. He turns round. Then he turns round again. Which way does he face now?
The board, the way he started
- Positive number
- A number more than zero. No sign means plus.
+
- Negative number
- A number less than zero. It has a minus sign.
−
- Same signs
- Two plus signs or two minus signs.
++−−
- Different signs
- One plus sign and one minus sign.
−++−
Are the signs the same or different?
−3 × −5Same
4 × −2Different
−6 × 3Different
What comes next?
- 3 × 3=9
- 2 × 3=6
- 1 × 3=3
- 0 × 3=0
- −1 × 3=−3
- −2 × 3=−6
down 3 each time
- −3 × 3=−9
- −3 × 2=−6
- −3 × 1=−3
- −3 × 0=0
- −3 × −1=3
- −3 × −2=6
up 3 each time
samedifferent
++→ same → +−−→ same → +−+→ different → −+−→ different → −
signnumber
- 1Same or different?A counter for each sign. No sign means plus.
- 2Pick the sign.Same: plus. Different: minus.
- 3Do the numbers.Times as normal. Put the sign in front.
Work out −4 × 5
1Same or different?−+→samedifferent
2Pick the sign.−
3Do the numbers.4 × 5 = 20
Answer−20
Work out −3 × −10
1Same or different?−−→samedifferent
2Pick the sign.+
3Do the numbers.3 × 10 = 30
Answer30
Work out −4 × 5
1Same or different?−+→samedifferent
2Pick the sign.−
3Do the numbers.4 × 5 = 20
Answer−20
1Same or different?2Same + Different −3Do the numbers.
Work out 5 × −5
1Same or different?+−→samedifferent
2Pick the sign.−
3Do the numbers.5 × 5 = 25
Answer−25
Work out −4 × 5
1Same or different?−+→samedifferent
2Pick the sign.−
3Do the numbers.4 × 5 = 20
Answer−20
1Same or different?2Same + Different −3Do the numbers.
Work out −2 × −3
1Same or different?−−→samedifferent
2Pick the sign.+
3Do the numbers.2 × 3 = 6
Answer6
Work out −4 × 5
1Same or different?−+→samedifferent
2Pick the sign.−
3Do the numbers.4 × 5 = 20
Answer−20
1Same or different?2Same + Different −3Do the numbers.
Work out 10 × −3
1Same or different?+−→samedifferent
2Pick the sign.−
3Do the numbers.10×3=30
Answer−30
1Same or different?2Same + Different −3Do the numbers.
1Work out −5 × 2
−+→samedifferent→−
5 × 2 = 10Answer−10
2Work out −4 × −4
−−→samedifferent→+
4 × 4 = 16Answer16
3Work out 3 × −3
+−→samedifferent→−
3 × 3 = 9Answer−9
4Work out −10 × −5
−−→samedifferent→+
10 × 5 = 50Answer50
samedifferent
++→ same → +−−→ same → +−+→ different → −+−→ different → −
signnumber
- 1Same or different?A counter for each sign. No sign means plus.
- 2Pick the sign.Same: plus. Different: minus.
- 3Do the numbers.Divide as normal. Put the sign in front.
Work out −15 ÷ 5
1Same or different?−+→samedifferent
2Pick the sign.−
3Do the numbers.15 ÷ 5 = 3
Answer−3
Work out −30 ÷ −10
1Same or different?−−→samedifferent
2Pick the sign.+
3Do the numbers.30 ÷ 10 = 3
Answer3
Work out −15 ÷ 5
1Same or different?−+→samedifferent
2Pick the sign.−
3Do the numbers.15 ÷ 5 = 3
Answer−3
1Same or different?2Same + Different −3Do the numbers.
Work out 12 ÷ −3
1Same or different?+−→samedifferent
2Pick the sign.−
3Do the numbers.12 ÷ 3 = 4
Answer−4
Work out −15 ÷ 5
1Same or different?−+→samedifferent
2Pick the sign.−
3Do the numbers.15 ÷ 5 = 3
Answer−3
1Same or different?2Same + Different −3Do the numbers.
Work out −18 ÷ −2
1Same or different?−−→samedifferent
2Pick the sign.+
3Do the numbers.18 ÷ 2 = 9
Answer9
Work out −15 ÷ 5
1Same or different?−+→samedifferent
2Pick the sign.−
3Do the numbers.15 ÷ 5 = 3
Answer−3
1Same or different?2Same + Different −3Do the numbers.
Work out −25 ÷ 5
1Same or different?−+→samedifferent
2Pick the sign.−
3Do the numbers.25÷5=5
Answer−5
Is it right?
Thumbs up: right. Thumbs down: wrong.
−3 × 4 = −12
Right−5 × −2 = −10
Wrong: same signs, plus20 ÷ −4 = −5
Right−7 × −2 = 14
Right−8 ÷ 2 = 4
Wrong: different signs, minus
Is −1 × −2 × −5 positive or negative? Work it out.
Negative: −10Two numbers multiply to make −10. They add to make 3. What are they?
5 and −2Find the missing number. ? ÷ −3 = 7
−21
Exit tickets to print
