The average weight of a group of 30 friends increases by 10 kg when the weight of additional 30 friends was added. If average weight of the whole group after including the additional 30 members is 40 kg, what is the average weight of the additional friends? Choose the correct answer
A) 50 kg
B) 60 kg
C) 61 kg
D) 62 kg
E) 91 kg

Rationale: let a = avg . wt . of additional 30 friends original total weight = ( 30 friends ) ( 30 kg avge ) = 900 kg ( 900 + 30 a ) / ( 30 + 30 ) = 40 kg avge a = 50 kg answer - a
Answer: A