Pannalal has done 1/3rd of a job in 20 days, Saiprasad completes the rest of the job in 10 days. In how many days can they together do the job?

Let total work to be done = 60 units

Work done by Pannalal in 20 days = $$\frac{1}{3} \times 60 = 20$$ units

Pannalal's efficiency = $$\frac{20}{20} = 1$$ unit/day

Remaining work = 60 - 20 = 40 units

Saiprasad completes 40 units in 10 days

=> Saiprasad's efficiency = $$\frac{40}{10} = 4$$ units/day

(Pannalal + Saiprasad)'s 1 day's work = 1 + 4 = 5 units/day

$$\therefore$$ Time taken by them together to do the job = $$\frac{60}{5} = 12$$ days

=> Ans - (A)