Answer : 4. "6"
Explanation :

Answer: D) 6 Explanation: Let us assume Amount be 100 Rs and we calculate in CI  First year 60% of 100 = 60 amount (100+60) is 160  Second year 60% of 160 = 96 amount (160+96) is 256  Third year 60% of 256 =153.6 amount (256+153.6) is 409.6  Here the Amount of 100 Rs is quadrapled in 3 years.  One year contains 2 half years  Three year has 6 half years.  Therefore,  It takes 6 half years.