The speed of a bus increases by 2 km after every one hour. If the distance travelling in the first one hour was 35 km. what was the total distance travelled in 12 hours?
Pick one.
A) 233  B) 552  C) 376  D) 287  E) 166

Rationale: given that distance travelled in 1 st hour = 35 km and speed of the bus increases by 2 km after every one hour hence distance travelled in 2 nd hour = 37 km hence distance travelled in 3 rd hour = 39 km . . . total distance travelled = [ 35 + 37 + 39 + . . . ( 12 terms ) ] this is an arithmetic progression ( ap ) with first term , a = 35 , number of terms , n = 12 and common difference , d = 2 . the sequence a , ( a + d ) , ( a + 2 d ) , ( a + 3 d ) , ( a + 4 d ) , . . . is called an arithmetic progression ( ap ) where a is the first term and d is the common difference of the ap sum of the first n terms of an arithmetic progression ( ap ) , sn = n 2 [ 2 a + ( n − 1 ) d ] where n = number of terms hence , [ 35 + 37 + 39 + . . . ( 12 terms ) ] = s 12 = 122 [ 2 × 35 + ( 12 − 1 ) 2 ] = 6 [ 70 + 22 ] = 6 × 92 = 552 hence the total distance travelled = 552 km answer : b
Answer: B