Suppose you work at a bowling alley. after work one day, you decide to line up bowling pins in a triangular

1) We are given that every row has one extra pin than the last one and since there are four rows and the First row start with 1 pin then the total number of pins in four rows would be- 1+2+3+4= 10

2) To complete 10 rows the total number of pins needed would be-  

Applying arithmetic progression to find out Sn = n/2 (2a + (n-1) d) = 5 x (2+9) =55

3) Now for 100 rows applying same formula again Sn = n/2 (2a + (n-1) d) = 50 x (2+99) =5050

4) Now for 1000 rows applying the formula Sn = n/2 (2a + (n-1) d) = 500x (2+999) =500500  

Ithink your answer is d

Ibelieve your answer is b.hope this : )