Name ________________________________________ Date __________________ Class__________________
Practice B
LESSON
5-5
Direct Variation
Tell whether each equation is a direct variation. If so, identify the
constant of variation.
1. y = 3x _________________
2. y = 2x − 9 _________________
3. 2x + 3y = 0 _________________
4. 3y = 9x _________________
Find the value of
y
for each ordered pair. Then, tell whether each
x
relationship is a direct variation.
5.
x
6
15
21
y
2
5
7
6.
y
x
x
6
10
25
y
24
40
100
y
x
________________________
Find k:
_________________________
Find k:
y = kx
(
=k
10
15
20
y
3
5
9
________________________
9. The value of y varies directly with x,
1
and y =
when x = 5.
2
Find y when x = 30.
Use k to find y:
y = _____
x
y
x
8. The value of y varies directly with x,
and y = −18 when x = 6.
Find y when x = −8.
_____
7.
Use k to find y:
) (_____ )
y = kx
(
y = _____
y = __________
_____
=k
y=
) (_____ )
__________
10. The amount of interest earned in a savings account
varies directly with the amount of money in the account.
A certain bank offers a 2% savings rate. Write a direct
variation equation for the amount of interest y earned
on a balance of x. Then graph.
_________________________________________
11. Another bank offers a different savings rate. If an
account with $400 earns interest of $6, how much
interest is earned by an account with $1800?
_________________________________________
Original content Copyright © by Holt McDougal. Additions and changes to the original content are the responsibility of the instructor.
5-44
Holt McDougal Algebra 1
14. y = 18x
Practice B
1. yes; 3
3. yes; –
5.
7.
2. no
2
3
1 1 1
; ;
3 3 3
yes
3 1 9
; ;
10 3 20
no
1
1
9.
; 30;
;3
10
10
4. yes; 3
6. 4; 4; 4
yes
8. –3; –8;
–3; 24
Review for Mastery
10.
4
3
1. no
2. yes;
3. yes; –3
4. yes; –
5. yes; 3.5
6. no
7. 40
8. –8.75
1
2
9.
y = 0.02x
11. $27
Practice C
1. yes; –2
2. yes; 2
5. no
2. no
y = 2.13x
5
4. yes;
9
6. no
Challenge
1. a. y = 5t, 40 minutes
7. yes; the ratio of y to x is –6 for each
ordered pair.
b. y = 10t, 20 minutes
c. y = 15t, 13
8. no; the ratio of y to x is not the same for
each ordered pair.
1
minutes
3
2. a. y = 15t
9. yes; the ratio of y to x is 1.5 for each
ordered pair.
b. y = 25t
c. y = 30t,
10. no; the relationship can not be expressed
in the form y = kx.
3. a. Q = 500 + 30t – 35t
b. emptying at 5 gallons per minute
11. 28
c. after 100 minutes, the tank will be empty
12. 5
13. y = 48x
Original content Copyright © by Holt McDougal. Additions and changes to the original content are the responsibility of the instructor.
A57
Holt McDougal Algebra 1