As they were walking, they encountered 49 lamps set in a circle, and found a tool that can toggle the state (on/off) of any set of 5 consecutive lamps. Tintin has to apply this tool sev- eral times to toggle the state of a single lamp. What are the possible no. of times Tintin would have to use this tool to achieve this?

Options

A. 25
B. 32
C. 40
D. 49

Explanation

Toggle all the doors except 5th, 10th, 15th, 20th, 25th, 30th, 35th, 40th, 45th, 49th  This way, Only Door 1 will be opened and all others closed. 
That means minimum steps required are 39 ….. So any odd number equal to or greater  than 39 is the possible steps   So 49 steps is the answer