120 coins of 50 paise.
.
For each 8 rupees, there is 4 rupees in 50 paise coins and 3 rupees in 25 paise coins, thus the coins ratio is:
8 rupees : 4 / 0.50 = 8 coins of 50 paise ; 3 / 0.25 = 12 coins of 25 paise => 8 : 8 : 12 coins.
Of each (8+8+12=) 28 coins, there are 8 coins of 50 paise.
There are 420 coins, thus 420 / 28 * 8 = 120 coins of 50 paise (+ 120 rupees + 180 coins of 25 paise).