The seventh line will be having 4 marbles which can be determined by taking the given data as an arithmetic progression with the first term as 1 and the common difference -1. Hence, option B is the right choice.
What is an Arithmetic Progression?
An arithmetic progression (A.P.) is a series where every term is the sum of the previous term and a common difference.
The first term of an arithmetic progression is denoted by a, and its common difference is denoted by d. The n-th term of an arithmetic progression can be found using the formula
n-th term = a + (n-1)d.
How do we solve the given question?
We are given a pattern, starting with 10 marbles and every consecutive line has 1 less marble than the previous line. We are asked to find the number of marbles in the 7th line.
This can be seen as an arithmetic progression with the first term a = 10, and the common difference d = -1.
We are asked to find the number of marbles in the 7th line. This can be taken as the 7th term of the given arithmetic progression.
n-th term = a + (n-1)d
or, 7th term = 10 + (7-1)(-1) = 10 + 6(-1) = 10 - 6 = 4.
∴ The seventh line will be having 4 marbles which can be determined by taking the given data as an arithmetic progression with the first term as 1 and the common difference -1. Hence, option B is the right choice.
Learn more about an arithmetic progression at
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