Total money = Rs.[600*(25/100)+1200*(50/100)]= Rs. 750.
25 paise coins removed = Rs. (600*12/100) = 72.
50 paise coins removed = Rs. (1200*24/100)= 288.
Money removed =Rs.(72*25/100+288*50/100) = Rs.162.
Required percentage = (162/750*100)% = 21.6 %.