The speed of a freight train is 12 km / h less than the speed of a passenger train.

The speed of a freight train is 12 km / h less than the speed of a passenger train. Determinant of the time it takes for a freight train to pass a 52 km section, if a passenger train passes such a section faster than a freight train by 18 minutes.

Let n be the speed of a passenger train, then (n – 12) is the speed of a freight train.

The time for which a passenger train passes 52 km is equal to: 52 / p,

the time for which 52 km of freight train passes is equal to: 52 / (n-12).

One time differs from another by 18 minutes, equal to 18/60 = 3/20 hours. Let’s make an equation and solve it:

52 / n = 52 / (n – 12) + 3/10.

(52 * n – 52 * n + 52 * 12) = 0.3 * n ^ 2 – 3.6 * n.

0.3 * n ^ 2 + 3.6 * n – 624 = 0;

n ^ 2 + 12 * n – 2080 = 0.n1,2 = 6 + – √ (36 + 2080) = 6 + – √2116 = 6 + – 46, Take n = 52.

Freight train time: 52/40 = 1.3 (hours).