Cogito
Grade 5 Math · Chapter 2 · Lesson 1
Multiplying Large Numbers
The same four pieces, with bigger numbers.
10 problems · about 16 minutes · 5.NBT.B.5
What this lesson teaches
The child multiplies multi-digit whole numbers using partial products.
- Bigger numbers use the same splitting.
- Every piece is one partial product.
- Estimate first, so a wrong answer stands out.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
2 problemsReview — Rounding Decimals: Round 7.63 to the nearest whole number.
Answer 8
Why 8.
Review — Comparing Decimals to Thousandths: Which is bigger, 0.608 or 0.61?
Answer 0.61.
Why 0.610 beats 0.608.
Warm Up
Straightforward practice. Get the method working first.
4 problems124 × 12 = ?
Answer 1488
Why 1,488.
Why estimate before multiplying?
Answer It catches an answer of the wrong size.
Why The estimate tells you roughly what to expect.
132 × 4 = ?
Answer 528
Why 400 + 120 + 8.
45 × 23 = ?
Answer 1035
Why 800 + 100 + 120 + 15.
Build It Up
The same ideas with more to keep track of.
2 problems206 × 12 = ?
Answer 2472
Why 2,060 + 412.
Estimate 39 × 51 to the nearest ten.
Answer 2000
Why 40 × 50.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
2 problemsThe Stadium: 124 rows of 32 seats. How many seats?
Answer 3968 seats
Why 3,720 + 248 = 3,968.
The Delivery: 215 boxes of 24 pens. How many pens?
Answer 5160 pens
Why 4,300 + 860 = 5,160.