The function y = 55 - 2.8x models the amount of water in a bathtub while it is draining for x

minutes. Which of the following statements properly interprets a key feature of the model?

A. The bath is draining at a rate of 55 gallons per minute
B. The amount of water in the bath increases by 2.8 gallons each minute
C. Before any water drained, the bath contained 2.8 gallons of water
D. Before any water drained, the bath contained 55 gallons of water

1 answer

To interpret the function \( y = 55 - 2.8x \), we can analyze its components:

  • The variable \( y \) represents the amount of water in the bathtub (in gallons).
  • \( x \) represents the time in minutes.
  • The constant \( 55 \) indicates the initial amount of water in the bathtub before it starts draining.
  • The term \( -2.8x \) indicates that the water is draining at a rate of 2.8 gallons per minute.

Now, let's analyze the provided statements:

A. The bath is draining at a rate of 55 gallons per minute.

  • This statement is incorrect because the rate of drainage is -2.8 gallons per minute (not 55).

B. The amount of water in the bath increases by 2.8 gallons each minute.

  • This statement is incorrect because the amount of water decreases by 2.8 gallons each minute as time progresses.

C. Before any water drained, the bath contained 2.8 gallons of water.

  • This statement is incorrect because it does not reflect the initial amount. The function at \( x = 0 \) yields \( y = 55 \), not 2.8.

D. Before any water drained, the bath contained 55 gallons of water.

  • This statement is correct. When \( x = 0 \), \( y = 55 - 2.8(0) = 55 \), indicating that there were 55 gallons in the bathtub initially.

Thus, the correct interpretation is:

D. Before any water drained, the bath contained 55 gallons of water.