George's home is 20 miles from his place of work. One day as he is dri

George's home is 20 miles from his place of work. One day as he is driving home from work, his car breaks down when he is 5 miles from work. He starts walking toward his home at an average rate of 4 miles per hour. If d represents his distance from home, in miles, and t represents the time, in hours, that he has been walking, which of the following gives d in terms of t ?

A.​ d = 15 - 4t​
B.​ d = 20 - 4t​
C.​ d = 4t - 15​
D.​ d = 4t - 20​
E.​ d = 4t + 5

You can either solve this question by plugin approach or by forming an equation connecting d and t, where d represents his distance from home and t represents his walking time in hours.

#1 : Plugin approach

It's given that the distance between George's home and his workplace is 20 miles. When his car breaks down he is 5 miles away from work. That means he needs to walk 15 miles to reach home.

So we can say that the value of 'd' should be 15 miles when t =0.

Why don't we plugin these values and cross-check how many options will satisfy this condition? Let's try it out

A.​ d = 15 - 4t​ ==> t =0, d = 15
B.​ d = 20 - 4t​ ==> t =0, d = 20 Eliminated
C.​ d = 4t - 15​ ==> t =0, d = -15 Eliminated
D.​ d = 4t - 20​ ==> t =0, d = -20 Eliminated
E.​ d = 4t + 5 ==> t =0, d = 5 Eliminated

The above condition is only satisfied in Option A. Hence, Option A is the correct answer.

#2 Forming the equation

We know that George needs to walk 15 miles to reach home from the breakdown point. He walks at an average speed of 4 miles /hr.

Distance covered by George by walking 't' hours = 4t

The remaining distance left to reach home i.e d = 15 -4t


Option A is the correct answer.


Thanks,
Clifin Francis,
GMAT Mentor