Activity 8.1: Direct Variation

In a direct variation, y=39 when x=3. Find the value of y when x=2.

• 26
• 3
• 58.5
• 2

Is this a direct variation? y=2x

• Yes
• No

Is this direct variation?

• Yes
• No

Write the equation for the table given.

• y = 1/3x
• y = 3x
• y = 1/2x

The number of kilograms of water in a person’s body varies directly as the person’s mass. A person with a mass of 90 kg contains 60 kg of water. How many kilograms of water are in a person whose mass is 75 kg?

• 50 kg water
• 72 kg water
• 94 kg water
• 150 kg water

Does this illustrate direct variation? y = 7x + 3

• Yes
• No

If y varies directly as x and y = 18 when x = 3, Find y when x = 7.

• 16
• 34
• 42
• 49

The electric power P varies jointly as the resistance R and the square of the current I can be written as

• P = RI²
• P = RI
• P = I/R
• P = kRI²

If y varies as the square of x and y=8 when x=1, find y when x=3.

• 24
• 72
• 8/3
• 3/8

Which of the given graphs is a direct variation?

• A
• B
• C
• D