Transcript 2-lesson-2

Lesson 2.2
I can estimate multi-digit products by rounding factors to a
basic fact and using place value patterns.
48,625- Say the number.
Between which two ten thousands is 48,625?
40,000 and 50,000.
What’s the midpoint for 40,000 and 50,000?
45,000.
Would 48,625 fall above or below 45,000?
Above.
48,625 ≈ ______ What’s 48,625 rounded to the nearest ten thousand?
50,000.
Repeat the process for thousands, hundreds, and tens.
Holden practices guitar 1 hour a day for 2 years. Lexy
Practices the guitar 2 hours more than Holden. How
many more minutes does Lexy practice the guitar
than Holden over the course of 2 years?
Holden practices guitar 1 hour a day for 2
years. Lexy Practices the guitar 2 hours more
than Holden. How many more minutes does
Lexy practice the guitar than Holden over the
course of 2 years?
How many minutes in an hour?
How many days in a year?
What operation:
60
min
365
Days
addition and multiplication
,!
365 x 2= 730
H
B
?
students do
we have in
class? 22
How many
classes in the
20
Do all the classes
have exactly 22
students?
How can we find a
number that is close to
the actual number of
We could Estimate how many
students are in each class! Let’s do
it!
What number could we use to
estimate each class?
Let’s use our class
22 is a bit difficult to multiply in my head. What
number would be a reasonable number to
multiply to make it easier?
2O
2O X 20 = 400 2 X 2 IS 4. Then you multiply it by 10 and
10. (4x10) x 10 = 4 x 100
about 400 elementary
students. Estimates can
help us understand a
product when we
multiply the original
numbers! Yay!
Check it out:
456 x 42
Suppose I don’t need to know the exact
product, just an estimate.How could I round
the factors to estimate the product?
How it works
Step 1
Step 2
Step 3
456 × 42 =___
You could:
You could:
round to the nearest
10. You’d get 460 x
40. But that’s still pretty hard
round to the hundreds
place. 500 x 40 is just
like we did in the
previous lesson!
How could I round the
factors to estimate the
product?
to do in my head.
500 x 40=
much
easier
5 hundreds x 4 tens
5 x 4 x 100 x 10
20 x 1000=
20,000
Try this one with a partner on your
boards:
4,560 x 42
What could you round these 2
numbers to?
5,000 X 40 =
5X4 = 20, Then add 4
zeros.
5,000 X 40 = 200,000
Another one!
4,560 x 420
What could you round these 2
numbers to?
5,000 X 400 =
5X4 = 20, Then add 5
zeros.
5,000 X 400 = 2,000,000
Rapid Fire! GO!
1.
1,320 x 88
1,300 x 90 = 117,000
or
1,000 x 90 = 90,000
2.
13,205 x 880
13,000 x 900 = 11,700,000
or
10,000 x 900 = 9,000,000
3.
3,120 x 880
3,000 x 900 =
2700,000
PROBLEM SET TIME!
Must Dos:
1. b. and c.
3.
2. c. and d.
4. c
and 5.
Examples
Check your
answers: