d = R X T

Here is a math problem Alexander, nine, and I had today. Algebra 1.

A train running 1320 miles in 24 hours starts ½ hours late. How much must it increase its speed to arrive on time?

Because the train starts the trip ½ hours late, it must traverse the entire distance in only 23 and 1/2 hours.

Two versions of the distance, rate, time problem:
(1) D = R x T
(2) average velocity = distance/time

Using the second version...

v = 1320/23.5
v = 56.2 mph

If the train had NOT started late,
v = 1320/24
v = 55 mph

56.2 - 55 = 1.2

So, the train must increase its speed by 1.2 mph over the other trip speed.