7th Grade Math

Find Slope

PHYSICAL SCIENCE The table below shows the relationship between

the number of seconds y it takes to hear thunder after a lightning

strike and the miles x you are from the lightning.

Miles (x) 01 2345

Seconds (y) 0 5 10 15 20 25

Graph the data and find the slope. Explain what the slope represents.

slope =

change in y

_

change in x

Definition of slope

Seconds

15

20

25

30

10

5

0 123456

Miles

Distance from

Lightning Strike

= _^255 - -^153 Use (3, 15) and (5, 25).

= _^102 secondsmiles

= _^51 Simplify.

So, for every 5 seconds between a

lightning flash and the sound of

thunder, there is 1 mile between

you and the lightning strike.

a. PLANTS Graph the data about plant

Week Plant Height (cm)

1 1.5

23

3 4.5

46

height for a science fair project. Then

find the slope of the line. Explain

what the slope represents.

Interpret Slope

BANKING Renaldo opened a savings

Amount ($)

Week

40

80

120

160

200

240

280

320

360

123456789

Renaldo’s Savings Account

account with the $300 he earned

mowing yards over the summer. Each

week he withdraws $20 for expenses.

Draw a graph of the account balance

versus time. Find the numerical value

of the slope and interpret it in words.

The slope of the line is the rate at

which the account balance falls,

or - _$20

1 week

. This is a negative slope
and therefore a negative rate of change.

b. Jessica buys a $10 pre-paid card for her cell phone. She pays a

rate of $0.05 per text. Draw a graph of the card balance versus

the number of text messages. Find the numerical value of the

slope and interpret it in words.

Everyday Use

Slope inclination or slant

Math Use

Slope the ratio of vertical

change per unit of

horizontal change; the

steepness of a line

Lesson 2C Slope 397

391_400_C07_L2_895130.indd 397 12/31/09 4:26 PM