Ajay, Bharat and Chandu can complete a piece of work in 24 days, 30 days, and 32 days, respectively. Ajay and Chandu work on the first day and Bharat completes the same work the next day. If they work in this way, in how many days can they complete the work?

Let's take the original work to be a multiple of the LCM of 24, 30 and 32; that would be 480x.

Now the efficiencies of Ajay, Bharat and Chandu are 20x, 16x and 15x units/day respectively. 

In the process defined in the question, we can add up the efficiencies of Ajay and Chandu, since they always work together, giving us an efficiency of 35x units/day. 
The next day, Bharat does 16x units/day.

In two days, these three do a total of 51x units/two-day.

So, in 9 days(18 days), all three can do a work of 51x*9 = 459x units.

Now, the remaining work is 480x-459x = 21x

The efficiencies of Ajay and Chandu, since they always work together, giving us an efficiency of 35x units/day.

They work together and complete the work in 21x/35x = 0.6 days

Option A is $$18\ \frac{21}{35}$$, this 21/35 is nothing but 0.6
So we can conclude that the answer would be Option A, without calculating the exact value.