This app deals with the problem about distance, time and speed. When two values are in, you can get the remaining one by calculating automatically.

How to use
There are three editable areas on the screen. Green is distance, blue is time, red is speed.
Tap one to make it acceptable and enter a value using the numbers below.
When two values are in, a button to calculate the remaining one comes up. You can make the last one calculated by tapping it.

Fine things
If a calculation is not divisible clearly, a mark is added to the end of numbers.
When you enter two values, it may not display the button to calculate because of out of range calculable.
There is a paid version notice at the bottom of the screen. Tap to see the description of it if interested.