Cogito
Grade 3 Math · Chapter 3 · Lesson 10
Two-Step Problems With a Letter
Naming the number you do not know yet.
10 problems · about 15 minutes · 3.OA.D.8
What this lesson teaches
The child solves two-step word problems using the four operations, writing an equation with a letter for the unknown.
- A letter stands for a number you have not found yet.
- Do the multiplication or division step first.
- Estimate to check the answer is sensible.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
2 problemsReview — Multiplication and Division Fluency: 7 × 6 = ?
Answer 42
Why 7 × 6 = 42.
Review — Patterns in the Times Tables: Is 8 × 7 odd or even?
Answer Even
Why An even factor makes the product even.
Warm Up
Straightforward practice. Get the method working first.
3 problems8 × 5 − 14 = ?
Answer 26
Why 8 × 5 = 40, and 40 − 14 = 26.
What does a letter stand for in an equation?
Answer A number you have not found yet.
Why The letter names the number you are looking for.
7 × 4 − 8 = ?
Answer 20
Why Multiply first.
Build It Up
The same ideas with more to keep track of.
1 problem45 ÷ 5 + 6 = ?
Answer 15
Why Divide first.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
4 problems6 × 6 − 10 = ?
Answer 26
Why 36 − 10.
The Bookshop: 5 shelves hold 8 books each. 12 books are sold. How many are left?
Answer 28 books
Why 40 − 12 = 28.
The Party Bags: 36 sweets are shared into 6 bags. Then 2 sweets are added to one bag.
Answer 8 sweets in that bag
Why 6 + 2 = 8 sweets.
The Coins: Ana has 3 bags of 9 marbles and loses 7. How many are left?
Answer 20 marbles
Why 27 − 7 = 20.