Topic 3 Multiply 2 and 3 Digit

2 by 2

100

24 × 13 =

312

200

 47 × 26

1,222

300

32 × 45

1,440

400

89 × 57

= 5,073

500

73 × 29 

= 2,117

3 by 2

100

 123 × 4

492

200

 134 × 12

1,608

300

215 × 13 

= 2,795

400

 307 × 46 

14,122

500

 412 × 39

= 16,068

Estimate

100

 28 × 43 (round each to nearest ten)

30 × 40 = 1,200

200

316 × 27≈ 

(nearest hundred for first, nearest ten for second then multiply)

≈ 300 × 30 = 9,000

300

79 × 64

 80 × 60 = 4,800

400

 498 × 203 ≈ 

(round each to one significant digit)

≈ 500 × 200 = 100,000

500

Give me an over estimate and and underestimate for

 78 × 46

over 

80 × 50 = 4,000

under

 70 × 40 = 2,800

Multiply using zero

100

50 × 6

300

200

 607 x 5 =

 = 3,035

300

204 × 30

6,120

400

 1,205 × 20

 24,100

500

Write an equation and solve 10³  x 240

1000 x 24

240,000

Vocabulary

100

Break factors into place-value parts, multiply each pair, then add.

Partial products (definition):

200

A column method that multiplies digits and carries values by place value.

It's efficient for paper-and-pencil computation and organizes carries clearly.

Standard algorithm

300

This is an example of

78 → 70, 46 → 40 ⇒ 70 × 40 = 2,800

How do you know?

Underestimate example for 78 × 46:

Shows why front-end can give a lower estimate.

400

What kind of estimate would this be 

356 → 400, 19 → 20 ⇒ 400 × 20 = 8,000

and why?

356 → 400, 19 → 20 ⇒ 400 × 20 = 8,000 (overestimate).

Because I rounded up so my answer is more then it will actually be 

500

What is the difference between using an area model and the standard algorithm. 

What is one similarity?

Difference: area models break each factor into place-value part

The standard algorithm organizes digit-by-digit multiplication with carries, which is efficient for speed and compact work.

similar: both use partial products