Question

On a drive from one city to​ another, the person averaged 51 mph. If he had been able to average 72 ​mph, he would have reached his destination 7 hrs earlier. What is the driving distance between one city and the​ other?

Answer 1

Answer: 1224 miles

Explanation:

Given

the average speed of a person is 51 mph

If speed is increased to 72 mph, he would have reached 7 hr earlier

Suppose d and t be the distance and time taken

`\Rightarrow t_1=(d)/(51)`

If the speed is 72 mph

`\Rightarrow t_2=(d)/(72)`

Also,
`t_1-t_2=7`

`\Rightarrow (d)/(51)-(d)/(72)=7\\\\\Rightarrow (1)/(51)-(1)/(72)=(7)/(d)\\\\\Rightarrow (24-17)/(1224)=(7)/(d)\\\\\Rightarrow (7)/(1224)=(7)/(d)\\\\\Rightarrow d=1224\ miles`