Transcript Mental Math: Estimate Products

5-Minute Check
1) 5 x 7
2) 7 x 70
3) 9 x 20
4) 4 x 800
5) 6 x 8000
6) The each person to eat for one week
is $200. Find the total cost for a family
of 5 to eat for one week.
Mental Math: Estimate
Products
Objective
By the end of this lesson, you will be able to
estimate products by rounding factors and using
easier numbers and then finding the product
mentally.
Essential Question: What strategies can you
use to multiply by a 1-digit number?
N.S. 1.3 - Round whole numbers through the
millions to the nearest ten, hundred, thousand,
ten thousand, or hundred thousand.
Explore
What is a reasonable estimate for 6 x 22?
Talk with your table to find an estimate for 6 x
22. Think about what you have learned
yesterday about multiplying by ten.
Explain
Anyone willing to share their strategies?
Do you think the exact answer for 6 x 22
is greater or less than your estimate?
Why?
Explain why finding an estimated answer
is sometimes better than finding an exact
answer.
More Examples
Try these problems:
3 x 38
5 x 78
7 x 42
Problem
An African elephant is the largest living land mammal. It
uses its trunk to pick up objects that weigh up to three
times as much as a 175-pound person. About how much
weight can an African elephant pick up with its trunk?
Step 1 - Round the greater factor to the nearest
hundred.
3 x 175
3 x 200
Step 2 - use mental math.
3 x 2 = 6 (basic fact)
3 x 20 = 60
3 x 200 = 600
Another Problem
In one day, an African elephant eats 9
bags of food. Each bag weighs 57
pounds. How many pounds of food does
the elephant eat?
9 x 57
Use mental math.
9 x 6 = 54 (basic fact)
9 x 60 = 540
5 x 7,441
7 x $6.68
9 x 820
4 x 32
7 x 98
3 x 415
6 x $3.25
9 x 6,221
6 x 281
4 x 2,509
Assignment
Blue Group – Blue Page
Everyone else – page 270 - #’s 9-25
Get them all correct - no Math homework