Not exactly sure, the context is not clear to me, but delta * 50 is not that large.
A delta is typically 1 / FPS, so if it's 60, that's 16ms or .0166666666 and so on. Times 50 it comes out like .833333. So that's like 83% of the distance between any two numbers.
You may want to go learn more about fixed time steps and how game loops utilize them. Delta is something of a scalar for a slice of time time. It will chop up the values that will add up to one second of game time, based on the frame rate you've decided.
With lerping for animation, tweening, easing, whatever you like to call it, your t value is like a knob that you control. So how much time it takes to go from 0 to 1 or if you use the full range is up to you. It's something only you as the creator can decide.
The values and time are up to what you think looks best. And there is are other methods that use curves instead of a linear progression. These can appear more organic, or interesting.
If you need to play around with that there is a decent site for applying various interpolations to X,Y cursor movement at this site: http://gizma.com/easing/
Though it's best to just dump out the values and comb over the actual steps one by one to best understand. I recommend also using ending numbers like 1, 10, or 100, so your results can also be viewed as percentages.