☰ Year plan · Mathematics

Subtracting on a number line and by parts

Week 23 Β· Subtracting on a number line and by parts Β· 3 lessons
1

Hop back on the number line

Discover Mathematics P2: Term 2, Lessons 91–100
GoalSubtract by hopping back on a number line, in tens and ones.
New words
hop back Β· move to a smaller number on the number linedifference Β· the answer to a subtractionsubtract Β· take one number away from another
Explanation

To subtract on a number line, start at the first number and hop back. For 17 βˆ’ 5, start at 17 and hop back 5 steps. You land on 12, so 17 βˆ’ 5 = 12. For bigger numbers use bigger hops. For 38 βˆ’ 15, hop back 10 to 28, then hop back 5 to 23. So 38 βˆ’ 15 = 23. Sometimes it helps to land on a ten first. For 52 βˆ’ 9, hop back 2 to 50, and then hop back 7 to 43. So 52 βˆ’ 9 = 43. The place where you finish is the difference.

05101520βˆ’5
Worked examples
7891011121314151617181920βˆ’5
17 βˆ’ 5: start at 17 and hop back 5. You land on 12.
2025303540βˆ’10βˆ’5
38 βˆ’ 15: hop back 10, then hop back 5. You land on 23.
40455055βˆ’2βˆ’7
52 βˆ’ 9: hop back 2 to reach 50, then hop back 7. You land on 43.
Class activity

Number line on the floor. Draw a number line from 0 to 30 with chalk, or lay paper numbers on the floor. Stand on a number such as 25 and hop back the steps called by a partner, for example 4, then 10. Say where you land and write the subtraction.

Practice
1
Use the number line to find 15 βˆ’ 9.
0481216βˆ’9?
2
Find 18 βˆ’ 12 on a number line.
3
Find 37 βˆ’ 16.
2025303540βˆ’10βˆ’6?
4
Find 28 βˆ’ 8. Where do you land?
5
Karim says 52 βˆ’ 9 = 41. Use hops to check.