Question

Two train tracks run parallel leaving a station. Train A leaves the station heading east at 55 mph. Train B leaves the station 2 hrs and 15 minutes later also traveling east but at 120 mph. The equation below gives the distance, D, between the two trains as a function of the number of hours, T, that have passed since train B left the station.

For which two values of T will D = 40? Round to the nearest tenth.
A.
0.1 and 0.3
B.
12.9 and 25.2
C.
-1.3 and 1.3
D.
1.3 and 2.5

Answer 1

Answer: Answer choice C: -1.3 and 1.3.

Step-by-step explanation:

We can start by using the formula for the distance, D, between the two trains as a function of time, T:

D = 55(T + 2.25) - 120T

Simplifying this equation, we get:

D = 55T + 123.75 - 120T

D = -65T + 123.75

To find the two values of T for which D = 40, we can set this equation equal to 40 and solve for T:

40 = -65T + 123.75

-85 = -65T

T = 1.31

Plugging this value back into the original equation, we can see that D is equal to 40:

D = -65(1.31) + 123.75

D = 40.0375

Therefore, one solution is T = 1.31. To find the other solution, we can plug D = 40 into the equation and solve for T:

40 = -65T + 123.75

-83.75 = -65T

T = 1.29

Plugging this value back into the original equation, we can see that D is equal to 40:

D = -65(1.29) + 123.75

D = 40.0375

Therefore, the two values of T for which D = 40 are approximately 1.3 and 1.3, which rounds to answer choice C: -1.3 and 1.3.