How do I increase a number with 1 formula?

every tick:
sprite: set x to: self.x+50[/code:17eomtem]

But i want the movement slightly going faster.
So I added global var [i]num[/i]

[code:17eomtem]Every 1 second: 
system: add 1 to num[/code:17eomtem]

And changed the code from above to: (added "*num")
[code:17eomtem]every tick:
sprite: set x to: self.x+50*num[/code:17eomtem]

How do I do this without adding an extra global variable?

Set X to: Self.X + 50 + 100*[(Self.X-Start.X) / (Target.X-Start.X)][/code:34ho81xw]
(replace 100 by the number that should be added extra when the Sprite almost reached the target)

[i][(Self.X-Start.X) / (Target.X-Start.X)][/i] calculates the movement progress of the Sprite (0 at the beginning, 1 at the end) and multiplies it with [i]100[/i].
That way, the extra value gets higher, the more the Sprite has moved.

Again, this only works [i]if the Start and End values are known and set each time[/i].

B) Use a plugin, for example [url=https://www.scirra.com/forum/behavior-litetween_t70700]LiteTween[/url].