Question

suppose you have 1200 rupees to save.you have save some amount at 10% and the rest at 15% .how much should be saved at each rate to yield 12%on total amount saved

Answer 1

Total yield we want = 12 % of 1200 = 12 * 12 = 144 
Let  P be the amount saved at 10% and  (1200 - P)  will be saved at 15%

Total interest will be = 10*P/100 + 15 (1200 - P) /100 = 144

10 P + 18000 - 15 P = 14400
5 P = 3600
P = 720

So save 720 at 10%  and  480 at 15%