A farming field can be ploughed by 6 tractors in 4 days. When 6 tractors work together, each of them ploughs 120 hectares a day. If two of the tractors were moved to another field, then the remaining 4 tractors could plough the same field in 5 days. How many hectares a day would one tractor plough then?	Choose the correct choice from the following answers:	A) 144	B) 255	C) 148	D) 265	E) 320

Rationale: if each of 66 tractors ploughed 120120 hectares a day and they finished the work in 44 days , then the whole field is : 120 ⋅ 6 ⋅ 4 = 720 ⋅ 4 = 2880120 ⋅ 6 ⋅ 4 = 720 ⋅ 4 = 2880 hectares . let ' s suppose that each of the four tractors ploughed xx hectares a day . therefore in 5 days they ploughed 5 ⋅ 4 ⋅ x = 20 ⋅ x 5 ⋅ 4 ⋅ x = 20 ⋅ x hectares , which equals the area of the whole field , 2880 hectares . so , we get 20 x = 288020 x = 2880 x = 288020 = 144 x = 288020 = 144 . hence , each of the four tractors would plough 144 hectares a day . correct answer is a ) 144
Answer: A