1. Warm-Up: Find the value of x in each diagram.
3. A girl that is 5 ft tall casts a shadow 4 ft long. At the same time, a tree casts a shadow 24 ft long. How tall is the tree?
4. Order the measurements from smallest to largest: inch, mm, foot, cm, km, mile
1. ∆ABC ~ ∆MLK 34
30 ft
2. RSTU ~ WXYZ 7
mm, cm, in, ft, km, mi

2. Warm Up Continued Find each absolute value. 5. |–2| 6. |8.1|
5. |–2| |8.1|
7. |3 – 1.2| |7 – 10| 2
8.1
1.8 3

3. HW Check
p. 42 (1 – 4) (6 – 8) (14 – 17)
They are the same shape, but not necessarily the same size.
5.6 m
10 ft
5 ℎ = ;20 𝑓𝑡
6. 8m
7. 7 in
ℎ = ;37.8 𝑓𝑡
14. 9m ft ft
17. 4cm

4. If every dimension of the figure is multiplied by a scale factor:
If every dimension of a figure is multiplied by the same number, the result is a similar figure. The multiplier is called a scale factor.
If every dimension of the figure is multiplied by a scale factor:
Ratio of perimeters = scale factor
Ratio of Areas = (scale factor)2
Ratio of Volumes = (scale factor)3

5. Example 3A: Changing Dimensions
The radius of a circle with radius 8 in. is multiplied by 1.75 to get a circle with radius 14 in. How is the ratio of the circumferences related to the ratio of the radii? How is the ratio of the areas related to the ratio of the radii?

6. Example 3B: Changing Dimensions
Every dimension of a rectangular prism with length 12 cm, width 3 cm, and height 9 cm is multiplied by to get a similar rectangular prism. How is the ratio of the volumes related to the ratio of the corresponding dimensions?

7. Helpful Hint
A scale factor between 0 and 1 reduces a figure. A scale factor greater than 1 enlarges it.

8. Check It Out! Example 3
A rectangle has width 12 inches and length 3 inches. Every dimension of the rectangle is multiplied by to form a similar rectangle. How is the ratio of the perimeters related to the ratio of the corresponding sides? How is the ratio of the areas related to the ratios of the corresponding sides?

9. Example 4
A rectangle has an area of 300 square centimeters. After every dimension of the rectangle is multiplied by a scale factor, the new area is 2700 square centimeters. What was the scale factor?

10. Post-It Check
The lengths of the sides of a square are multiplied by 2.5. How is the ratio of the areas related to the ratio of the sides?
The ratio of the areas is the square of the ratio of the sides: (2.5)2 = 6.25

11. A precision is the level of detail in a
measurement and is determined by the
smallest unit or fraction of a unit that you
can reasonably measure.
The accuracy of a measurement is the closeness of a measured value to the actual or true value.
Tolerance describes the amount by which a measurement is permitted to vary from a specified value.

12. Example 1: Comparing Precision of Measurements
Choose the more precise measurement in each pair.
A. 0.8 km; m
0.8 km
Nearest tenth of a kilometer
830.2 m
Nearest tenth of a meter
A tenth of a meter is smaller than a tenth of a kilometer, so m is more precise.
B in.; 2.5 in.

13. Example 1: Continued
2.45 in.
Nearest hundredth of an inch
2.5 in.
Nearest tenth of an inch
A hundredth of an inch is smaller than a tenth of an inch, so 2.45 in. is more precise.
C. 100 cm; 1 m
100 cm
Nearest centimeter
1 m
Nearest meter
A centimeter is smaller than a meter, so 100 cm is more precise.

14. Check It Out! Example 1
Choose the more precise measurement in each pair.
1a. 2 lb; 17 oz.
2 lb
Nearest pound
17 oz
Nearest ounce
An ounce is smaller than a pound, so 17 oz is more precise.
1b m; 7.8 m.

15. Check It Out! Example 1 Continued
Nearest hundredth of a meter
7.8 m
Nearest meter
A hundredeth of a meter is smaller than a meter, so 7.85 m is more precise.
1c. 6 kg; 6000 g.
6 kg
Nearest kilogram
6000 g
Nearest gram
A gram is smaller than a kilogram, so 6000 g is more precise.

16. Example 2 : Comparing Precision and Accuracy
Ida works in a deli. She is testing the scales at the deli to make sure they are accurate. She uses a weight that is exactly 1 pound
and gets the following results:
Scale 1: lb
Scale 2: 1.01 lb
Scale 3: 0.98 lb
A. Which scale is the most precise?
Scales 2 and 3 measure to the nearest hundredth of a pound. Scale 1 measures to the nearest thousandth of a pound.

17. Example 2 : Continued
Because a thousandth of a pound is smaller than a hundredth of a pound, Scale 1 is the most precise.
B. Which scale is the most accurate?.
For each scale, find the absolute value of the difference of the standard mass and the scale reading.
Scale 1: |1.000 – 1.019| = 0.019
Scale 2: |1.000 – 1.01| = 0.01
Scale 3: |1.000 – 0.98| = 0.02
Because 0.01 < < 0.02, Scale 2 is the most accurate.

18. Check It Out! Example 2
A standard mass of 16 ounces is used to test three postal scales.
The results are shown below.
A. Which scale is the most precise?
Scales A and B measure to the nearest tenth of an ounce.

19. Check It Out! Example 2 Continued
Scale C measures to the nearest hundredth of an ounce.
Because a hundredth of an ounce is smaller than a thousandth of an ounce, Scale C is the most precise.
B. Which scale is the most accurate?
For each scale, find the absolute value of the difference of the standard mass and the scale reading.

20. Check It Out! Example 2 Continued
Scale 1: |16.00 – 16.3| = 0.3
Scale 2: |16.00 – 15.8| = 0.2
Scale 3: |16.00 – 16.07| = 0.07
Because 0.07 < 0.2 < 0.3, Scale C is the most accurate.

21. Lesson Quiz :
1. Choose the more precise measurement: 2.4 km; 2430 m
2430 m
2. Jorge works in a mail room. To test the accuracy of the scales in the mail room, he uses a weight that is exactly 8 oz. and gets the following results:
Scale 1: 8.02 oz
Scale 2: oz
Scale 3: oz
a. Which scale is the most precise? 2
b. Which scale is the most accurate? 3

22. Classwork:
P. 33 (4 – 5)
P. 34 (1 – 4)
P. 39 (1 – 6), (13 – 14)

23. Closing/HW:
Closing: You will have a vocabulary quiz tomorrow. Write down the words that you will be responsible for knowing.
HW: Textbook p. 44 (23) p. 49 (19 – 27) ALL