well, 50% is pretty much half.
you need 2500 for the deposit, you have 50% or half of that.
whatever% of anything is just (whatever/100) * anything.
50% of 2500 is just (50/100) * 2500 or 0.5 * 2500 or 1250.
how much more do you need? well, you need the other 50%.
50% of 2500 is just (50/100) * 2500 or 0.5 * 2500 or 1250.