1
Trading a ten
Discover Mathematics P2: Term 2, Lessons 91–100
GoalSubtract two-digit numbers when the ones need regrouping, by trading one ten for ten ones.
New words
regroup · trade one ten for ten onesdifference · the answer to a subtractionones · the single units in a numbertens · groups of ten in a number
Explanation
Take 27 away from 52. Look at the ones first. 2 ones cannot lose 7 ones, so trade 1 ten for 10 ones. Now there are 4 tens and 12 ones. Subtract the ones: 12 − 7 = 5. Subtract the tens: 4 − 2 = 2. The difference is 25, so 52 − 27 = 25. You can check by adding: 25 + 27 = 52.
Worked examples
41 − 18: the ones 1 cannot lose 8. Trade 1 ten: 3 tens and 11 ones, as in the picture. Then 11 − 8 = 3 and 3 − 1 = 2. So 41 − 18 = 23.
63 − 35: trade 1 ten for 10 ones, so 5 tens and 13 ones. Then 13 − 5 = 8 and 5 − 3 = 2. So 63 − 35 = 28.
70 − 24: there are no ones, so trade 1 ten for 10 ones. Now 6 tens and 10 ones. Then 10 − 4 = 6 and 6 − 2 = 4. So 70 − 24 = 46.
Class activity
Bundles of sticks. Make 4 bundles of 10 craft sticks with rubber bands and put 6 single sticks beside them. That is 46. Take away 28 sticks. You cannot take 8 singles from 6, so untie one bundle. Now count what is left and say the subtraction sentence.
Practice
1
Find 34 − 18.
34 − 18 = 16.
2
Karim has 82 stickers. He gives 47 to his class. How many are left?
82 − 47 = 35 stickers.
3
The picture shows 50 as 4 tens and 10 ones. Now find 50 − 23.
10 − 3 = 7 and 4 − 2 = 2, so 50 − 23 = 27.
4
Mariam says 65 − 29 = 44. Is she right? Check by adding.
No. 65 − 29 = 36. Check: 36 + 29 = 65.
5
73 is 7 tens and 3 ones. Write it as ___ tens and 13 ones.
6 tens and 13 ones.