Type 1 workers are 2.5 times as efficient as Type 2 workers. Twelve Type 1 workers can
complete a task in 10 days. How many days would it have taken 4 Type 1 and 15 Type 2 workers to do the same work?

The correct option is C.

12 Type1 workers completed=10 days
1 Type1 worker will complete=$$12\times 10$$=120 days
Since Type1 worker 2.5 times efficient than type2
1 type2 worker complete =$$2.5\times120$$=300 days
Total unit of job=L.C.M of (120 & 300)=600
1 Type1 worker unit of job in one day=$$\frac{600}{120}$$=5
1 type2 worker unit of job in one day=$$\frac{600}{300}$$= 2
Now, 4 Type1 workers job unit + 15 type2 workers job unit in one day=$$4\times 5+15\times 2$$=20+30=50
total time to complete job=  =12 days
$$\frac{600}{50}$$