One person can do a certain job in six days, a second person can do the same job in two days, and a third person can do this job in three days. how many days will they take to do the job together?
1 day
2 days
6 days

So here is how we answer this:
Given that:
Person A can finish job in 6 days
Person B can finish job in 2 days
Person C can finish job in 3 days.
So let us present it this way.
x/6 + x/2 + x/3 = number of days
Find common denominator which is 6.
x/6 +3x/6 + 2x/6 = days
6x/6 = days
x = 1 day.
Therefore, they can finish a certain job together in 1 day.
The correct answer would be the first option. Hope this helps.