A grocer purchased 200 kg of rice at Rs.25 per kg. He sold 80 kg of it at a gain of 10% and 40 kg at a loss of 4%. At what rate per kg should he sell the remainder to gain 8% on his total investment?
CP of Rice = 200 × 25
= Rs.5000
CP 0f 80 kg Rice = 80 × 25
= Rs.2000
SP of 80Kg rice sold at gain of 10%
= Rs.2200
CP of 40 kg Rice sold @4% loss = 40 × 25
= Rs.1000
SP of 40 Kg Rice sold @4% loss 
= Rs.960
SP of Rice for Gaining 8% on total value
= Rs.5400
Total Wt. of Rice Sold = 80 + 40 = 120 Kg
Remaining Wt. of Rice to be Sold
= 200 - 120
= 80 Kg
Total amount obtained from Selling Rice
= 2200 + 960
= Rs.3160
Difference of Amount = 5400 – 3160
= Rs.2240
New Rate of Rice will be = Rs.2240 / 80
= Rs.28
25