2 by 2
24 × 13 =
312
123 × 4
492
28 × 43 (round each to nearest ten)
30 × 40 = 1,200
50 × 6
300
Break factors into place-value parts, multiply each pair, then add.
Partial products (definition):
47 × 26
1,222
134 × 12
1,608
316 × 27≈
(nearest hundred for first, nearest ten for second then multiply)
≈ 300 × 30 = 9,000
607 x 5 =
= 3,035
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
32 × 45
1,440
215 × 13
= 2,795
79 × 64
80 × 60 = 4,800
204 × 30
6,120
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.
89 × 57
= 5,073
307 × 46
14,122
498 × 203 ≈
(round each to one significant digit)
≈ 500 × 200 = 100,000
1,205 × 20
24,100
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
73 × 29
= 2,117
412 × 39
= 16,068
Give me an over estimate and and underestimate for
78 × 46
over
80 × 50 = 4,000
under
70 × 40 = 2,800
Write an equation and solve 103 x 240
1000 x 24
240,000
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