In a row of 36 pupils, the first boy is followed by one girl, the second boy is followed by two girls, the third boy is followed by three girls and so on like this. What is the number of girls in the second half of the row ?

Options

A. 28
B. 9
C. 16
D. 15

Answer

D

Explanation

According to the pattern given in the question, there will be a total 8 boys and 28 girls.
`therefore` Number of girls = `n/2 [2a + (n − 1) d]`
`(because n=7, a = 1, d= 1) `
`=7/2 [2 xx 1 + (7 - 1) xx 10] = 28`.
The arrangement is as shown below: `{:("First half",,"Second half"),("BGBGGBGGGBGGGGBGGG","/","GGBGGGGGGBGGGGGGGB"):}`
So, the number of girls in the second half of the row = 15.