A highway is under construction. The workers have completed 2/5 of the total length. If the workers complete an additional 7.5 miles, then they would have completed 1/2 of the total length. What is the total length (miles) of this highway under construction?

Let us assume that the total length of the highway = X

From the question, we know that the workers have completed 2/5 of the total length. Then the distance upto which work is completed = 2X/5

On completing another 7.5 miles, the work would be complete by half.

So

2X/5 + 7.5 = X/2

(X/2) - (2X/5) = 7.5

(5X/10) - (4X/10) = 7.5

(5X - 4X) / 10 = 7.5

X/10 = 7.5

X = 7.5 * 10

= 75

So the total length of the highway under construction is 75 miles.