Cogito
Grade 2 Math · Chapter 1 · Lesson 4
Take From Ten to Subtract
Break the teen number apart and subtract from the ten.
10 problems · about 12 minutes · 2.OA.B.2
What this lesson teaches
The child subtracts within 20 by taking the subtrahend from the ten inside a teen number.
- Every teen number holds a ten.
- If the ones are too few, subtract from the ten.
- Then add the leftover ones back on.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
2 problemsReview — Make Ten to Add: 9 + 8 = ?
Answer 17
Why 9 + 1 + 7 = 10 + 7 = 17.
Review — Near Doubles: 8 + 9 = ?
Answer 17
Why 8 + 8 = 16, and one more makes 17.
Warm Up
Straightforward practice. Get the method working first.
4 problems15 − 8 = ?
Answer 7
Why 2 + 5 = 7.
Why take from the ten in 14 − 9?
Answer The 4 ones are too few to take 9 from.
Why There are not enough ones, so the ten is where the 9 has to come from.
12 − 9 = ?
Answer 3
Why 10 − 9 leaves 1.
14 − 8 = ?
Answer 6
Why 10 − 8 leaves 2.
Build It Up
The same ideas with more to keep track of.
2 problems17 − 9 = ?
Answer 8
Why 10 − 9 leaves 1.
13 − 7 = ?
Answer 6
Why 10 − 7 leaves 3.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
2 problemsSharing Stickers: Ana had 13 stickers and gave away 8. How many stickers does she have left?
Answer 5 stickers
Why 10 − 8 = 2, and 2 + 3 = 5.
The Bus Stop: 16 children were on the bus. 7 got off. How many children stayed on?
Answer 9 children
Why 10 − 7 = 3, and 3 + 6 = 9.