A group of college students had decided to complete a project in 10 days. As 2 students dropped out every day, the project got completed at the end of the 15th day. The number of students at the beginning of the project was:
Show answer & explanation
Correct answer: A
Explanation
The correct answer is option 1 i.e. 42.
Let the students at the beginning be x.
Sum of n terms = (n/2)(a + l)
where n is number of terms, a is first term and l is last term.
According to the given question,
x + (x - 2) + (x - 4) ..... + (x - 28) = x × 10
⇒ (15/2)(x + x - 28) = 10x
⇒ 15x - 210 = 10x
⇒ 5x = 210
⇒ x = 42