Ram, who is half as efficient as Krish, will take 21 days to complete a task if he worked alone. If Ram and Krish worked together, how long will they take to complete the task?
Choose one.
A) 16 days
B) 12 days
C) 8 days
D) 7 days
E) 18 days
Number of days taken by Ram to complete task = 21   Since Ram is half as efficient as Krish , Amount of work done by Krish in 1 day = Amount of work done by Ram in 2 days   If total work done by Ram in 24 days is 21w   Amount of work done by Ram in 1 day = w   Amount of work done by Krish in 1 day = 2w   Total amount of work done by Krish and Ram in a day = 3w   Total amount of time needed by Krish and Ram to complete task = 21w/3w = 7 days   Answer 7 days21 /3= 
<gadget id="calculator">21 /3</gadget>
<output>7</output>
7 days   Answer 7 days
<result>D</result>
Ram, who is half as efficient as Krish, will take 21 days to complete a task if he worked alone. If Ram and Krish worked together, how long will they take to complete the task?