Name ———————————————————————
SECTION
6
Date ————————————
Algebra
Lesson 14: Using Formulas
You can use formulas to solve many word problems. First, write the appropriate
formula. Then, substitute the values given for the variables. Finally, solve the
equation for the missing variable.
Here are three problems you can solve using the formula d 5 rt
(distance 5 rate 3 time). In each of them, we are solving for a different variable.
You drive a car for 4 hours at 55 miles per hour (mi/h).
How many miles do you drive?
d 5 rt
5 55 3 4
5 220 miles
EXAMPLE 2
You drive a car 300 miles at 60 miles per hour.
How many hours do you drive?
6. ALGEBRA
14. Using Formulas
EXAMPLE 1
Copyright © by McDougal Littell, a division of Houghton Mifflin Company.
d 5 rt
300 5 60t
t 5 5 hours
EXAMPLE 3
You drive a car 300 miles for 6 hours.
What is your average drinking rate?
d 5 rt
300 5 r 3 6
r 5 50 miles per hour
Practice: First Try
1. You drive a car 200 miles at 50 miles per hour. How many hours do you drive?
2. You drive a car for 3 hours at 65 miles per hour. How many miles do you drive?
3. You drive a car 120 miles for 3 hours. What is your average driving rate?
4. You drive a car for 4 hours at 60 miles per hour. How many miles do you drive?
McDougal Littell Middle School Math
Remediation Book Lesson 6.14
193
Name ———————————————————————
Date ————————————
Practice: Second Try
Use the formula d = rt.
1. You drive a car for 2 hours at 55 miles per hour. How many miles do you drive?
2. You drive a car 180 miles for 3 hours. What is your average driving rate?
3. You drive a car 270 miles at 60 miles per hour. How many hours do you drive?
4. You drive a car 232 miles for 4 hours. What is your average driving rate?
5. You drive a car 210 miles at 42 miles per hour. How many hours do you drive?
6. ALGEBRA
14. Using Formulas
Use the formulas for a square: P 5 4s and A 5 s 2.
6. Find the perimeter of a square with side length 8 ft.
7. Find the side length of a square with perimeter 20 cm.
8. Find the area of a square with side length 4 in.
9. Find the side length of a square with area 36 m2 .
10. Find the side length of a square with an area of 64 ft2.
11. A rectangle has length 9 in. and width 2 in. Find the perimeter and the area.
12. A rectangle has area 12 m2 and width 3 m. Find the length.
13. A rectangle has perimeter 28 cm and length 6 cm. Find the width and the area.
14. A rectangle has width 7 yd and perimeter 34 yd. Find the area.
Extend Your Skills
15. The formula for calculating simple interest is I 5 prt, where I is the amount of
interest, p is the principal amount invested, r is the annual rate of interest written as
a decimal, and t is time in years. Henry is going to put $2000 in a savings account
that has a 3% interest rate. If he wants to make $300 in interest, how long will he
need to leave the money in the account?
Puzzle
Alex is communicating online with his friend Ricardo, who lives in Spain. Ricardo
claims that it is a very hot day, at 40°C. Alex doesn’t think that sounds like a hot
9
temperature. Use the formula F 5 }5 C 1 32 to convert the temperature to °F.
Was Ricardo right?
194
McDougal Littell Middle School Math
Remediation Book Lesson 6.14
Copyright © by McDougal Littell, a division of Houghton Mifflin Company.
Use the formulas for a rectangle: P 5 2l 1 2w and A 5 lw.
!NSWER+EY
-iV̈œ˜ÊÈʏ}iLÀ>
iÃܘʣ{ÊÊ­««°Ê£™Î£™{®
*À>V̈Vi\Ê
ˆÀÃÌÊ/ÀÞÊÊ
£°HOURSÊÓ°MILESÊΰMIH{°MILES
-iVœ˜`Ê/ÀÞÊ
£°MILESÊÊÓ°MIHÊÊÊ
ΰHOURSÊÊ{°MIHx°HOURS
È°FTÊÊÇ°CMÊn°INʙ°MÊÊ
£ä°FT££°ININÊ£Ó°MÊÊ
£Î°CMCMÊÊ£{°FTÊÊÊ£x°YEARSÊÊ
*Õââi
9ES2ICARDOWASRIGHT)TIS&
Name ———————————————————————
SECTION
6
Date ————————————
Algebra
Lesson 14: Using Formulas
You can use formulas to solve many word problems. First, write the appropriate
formula. Then, substitute the values given for the variables. Finally, solve the
equation for the missing variable.
Here are three problems you can solve using the formula d 5 rt
(distance 5 rate 3 time). In each of them, we are solving for a different variable.
You drive a car for 4 hours at 55 miles per hour (mi/h).
How many miles do you drive?
d 5 rt
5 55 3 4
5 220 miles
EXAMPLE 2
You drive a car 300 miles at 60 miles per hour.
How many hours do you drive?
6. ALGEBRA
14. Using Formulas
EXAMPLE 1
Copyright © by McDougal Littell, a division of Houghton Mifflin Company.
d 5 rt
300 5 60t
t 5 5 hours
EXAMPLE 3
You drive a car 300 miles for 6 hours.
What is your average drinking rate?
d 5 rt
300 5 r 3 6
r 5 50 miles per hour
Practice: First Try
1. You drive a car 200 miles at 50 miles per hour. How many hours do you drive?
2. You drive a car for 3 hours at 65 miles per hour. How many miles do you drive?
3. You drive a car 120 miles for 3 hours. What is your average driving rate?
4. You drive a car for 4 hours at 60 miles per hour. How many miles do you drive?
McDougal Littell Middle School Math
Remediation Book Lesson 6.14
193
Name ———————————————————————
Date ————————————
Practice: Second Try
Use the formula d = rt.
1. You drive a car for 2 hours at 55 miles per hour. How many miles do you drive?
2. You drive a car 180 miles for 3 hours. What is your average driving rate?
3. You drive a car 270 miles at 60 miles per hour. How many hours do you drive?
4. You drive a car 232 miles for 4 hours. What is your average driving rate?
5. You drive a car 210 miles at 42 miles per hour. How many hours do you drive?
6. ALGEBRA
14. Using Formulas
Use the formulas for a square: P 5 4s and A 5 s 2.
6. Find the perimeter of a square with side length 8 ft.
7. Find the side length of a square with perimeter 20 cm.
8. Find the area of a square with side length 4 in.
9. Find the side length of a square with area 36 m2 .
10. Find the side length of a square with an area of 64 ft2.
11. A rectangle has length 9 in. and width 2 in. Find the perimeter and the area.
12. A rectangle has area 12 m2 and width 3 m. Find the length.
13. A rectangle has perimeter 28 cm and length 6 cm. Find the width and the area.
14. A rectangle has width 7 yd and perimeter 34 yd. Find the area.
Extend Your Skills
15. The formula for calculating simple interest is I 5 prt, where I is the amount of
interest, p is the principal amount invested, r is the annual rate of interest written as
a decimal, and t is time in years. Henry is going to put $2000 in a savings account
that has a 3% interest rate. If he wants to make $300 in interest, how long will he
need to leave the money in the account?
Puzzle
Alex is communicating online with his friend Ricardo, who lives in Spain. Ricardo
claims that it is a very hot day, at 40°C. Alex doesn’t think that sounds like a hot
9
temperature. Use the formula F 5 }5 C 1 32 to convert the temperature to °F.
Was Ricardo right?
194
McDougal Littell Middle School Math
Remediation Book Lesson 6.14
Copyright © by McDougal Littell, a division of Houghton Mifflin Company.
Use the formulas for a rectangle: P 5 2l 1 2w and A 5 lw.