Suppose 'David' have 200% more than initial investment of Chintu for a year. What will be the total interest earned by him if he invested his amount in a Mutual fund which offers 10% p.a. compound interest for 3 years?

ATQ, we can say that Let the investment of Anuj, Binod, and chintu is 3a, 5a and 7a. Investment of Anuj = 3a × 4 + (3a – 800) × 6 + (3a – 800 + 5x) × 2 = 46a – 6400 Rs.  Investment of Binod = 5a × 4 + (5a + 1000) × 6 + (5a + 11a) × 2 = 82a + 6000 Rs.  Investment of Chintu = 7a × 10 + (7a + 1.5a) × 2 = 87a Rs.  87a/(46a – 6400 + 82a + 6000 + 87a) = 145/358 3a × 358 = 5 × (215a – 400) 1074a = 1075a – 2000 a = 2000 Profit Ratio, Anuj : Binod : Chintu = (46 × 2000 – 6400) : (82 × 2000 + 6000) : (87 × 2000) Anuj : Binod : Chintu = (920 – 64) : (1640 + 60) : 1740  = 856 : 1700 : 1740  = 214 : 425 : 435 Hence required % will be  (214/1074) × 100  = ATQ, we can say that Let the investment of Anuj, Binod, and chintu is 3a, 5a and 7a. Investment of Anuj = 3a × 4 + (3a – 800) × 6 + (3a – 800 + 5x) × 2 = 46a – 6400 Rs.  Investment of Binod = 5a × 4 + (5a + 1000) × 6 + (5a + 11a) × 2 = 82a + 6000 Rs.  Investment of Chintu = 7a × 10 + (7a + 1.5a) × 2 = 87a Rs.  87a/(46a – 6400 + 82a + 6000 + 87a) = 145/358 3a × 358 = 5 × (215a – 400) 1074a = 1075a – 2000 a = 2000 Profit Ratio, Anuj : Binod : Chintu = (46 × 2000 – 6400) : (82 × 2000 + 6000) : (87 × 2000) Anuj : Binod : Chintu = (920 – 64) : (1640 + 60) : 1740  = 856 : 1700 : 1740  = 214 : 425 : 435 Hence required Interest earned by David is = [3 × 7 × 2000 × (1.13 – 1)] =  42000 × 0.331 =  Rs.13902