Bunuel wrote:

Working at their normal constant rates, 20 diggers can dig a 100-meter long trench in hard soil in 3 days. A construction company ordered the diggers to dig a 180-meter long trench in soft soil. If diggers can work 20% faster in soft soil than in hard soil, how many diggers are required to complete this task in 3 days?

A. 25

B. 28

C. 29

D. 30

E. 32

20 persons -- dig 100 m trench in

hard soil - in 3 days

1 person -- dig \(\frac{100}{20}\) trench in

hard soil - in 3 days

1 person -- digs 5 trench in

hard soil - in 3 days

1 person -- digs 5*1.2 trench in

soft soil - in 3 days

1 person -- digs 6 m trench in

soft soil - in 3 days

Required trench length : 180 m. 180 = 6 * 30.

So

30 persons -- dig 6*30 m trench in

soft soil - in 3 days

Answer: 30 persons.

D is desired answer