Pooja is twice as efficient as Nita and four times as efficient as Kavya. If Nita takes 30 days to finish some work, then find the time taken by Pooja and Kavya to do the same work together.

Since, Pooja is twice as efficient as Nita, she will take half the time taken by Nita to finish the work. So, time taken by Pooja to do the work = 30 ÷ 2 = 15 days And, Pooja is four times as efficient as Kavya, so Kavya will take four times the time taken by Pooja. So, time taken by Kavya to do the work = 4 × 15 = 60 days Let the total work be '60x' units. So, efficiency of Pooja = 60x ÷ 15 = '4x' units/day And, efficiency of Kavya = 60x ÷ 60 = 'x' units/day So, required time = 60x ÷ (4x + x) = 12 days Hence, option b.