MJ2
Ch 11.2 – Estimating Square
Roots
Bellwork
• Police officers can use a formula and skid marks
to determine the speed of a car. Use the formula
below to calculate how fast a car was going if it
left skid marks 83 feet long. Round to the
nearest tenth. (s= speed, d=distance)
s  39d
Note: You do not have to write the question. However, your
response should be in formula method format for full credit
Bellwork Solution
s  39d
1. Write the formula
s  39(83)
2. Substitute
s  3237
3. Do the math
s  56.9mph
Assignment Review
• Text p. 472 # 13 – 33
Before we begin…
• Please take out you notebook and get
ready to work….
• In the last lesson we looked at squares
and square roots…
• In today’s lesson we will look at
estimating square roots…in order to
estimate you will need to know the
perfect squares….
Objective 11.2
• Students will estimate square roots
Estimating
• Generally speaking, students have a
difficult time estimating…students do
not have a fully developed number
sense and really don’t get estimating…
• The goal of estimating is to get a
number that it is close to….we are not
looking for an exact number here…the
exact number is not important…
Estimating using a number line
• In the notes section of your notebook draw a
number line.
• Plot the perfect squares from 1 through 12 on
the number line
• When estimating the goal is to find out which
whole number the perfect square is close to…
• That will be your estimate…
• Let’s see what it looks like…
Number Line
• Your number line should look like this…
• To find the square root of a number find where it fits on a
number line
• Then determine the two numbers it fits between
• Determine which number it is closest to and look at the perfect
square for that number
1
4
9 16 25
36
49
64
81 100 121 144 169 196 225
Perfect Squares
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Example
Find the
75
The square root of 75 is between the square root of 64 and 81
Since 75 is closer to 81 than 64 the nearest whole number would be 9
The estimate of
1
4
would be 9
75
9 16 25
36
49
64
81 100 121 144 169 196 225
Perfect Squares
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Your Turn
• In the notes section of your notebook
estimate each square root to the nearest
whole number
Solutions
6
1.
39
2.
140
12
3.
106
10
Calculators
• You can also use a calculator to estimate a
square root to the nearest whole number
This is the square root key
Input the square root number and
press the square root key
You will get a decimal for an
answer.
Round the decimal to the nearest
whole number
Your Turn
• Using a calculator
estimate the
square roots to
the nearest whole
number
1.
131
2.
277
3.
3502
Summary
• In the notes section of your notebook
summarize the key concepts covered in
today’s lesson
• Today we discussed:
• Estimating square roots – how does that
work?
• Using a calculator to estimate square roots
– what do you do?
Assignment
• Text p. 477 # 13 – 28
Reminder
• This assignment is due tomorrow
• I do not accept late assignments
• This is probably the only assignment that I
will accept answers only!
• In this instance it’s kind of hard to show
your work when you are using a calculator