C. 33 marbles must be there in the sixth line.
How to elaborate the problem ?
There are 2 marbles in the 1st line, 3 marbles in the 2nd, 5 marbles in the 3rd and 9 marbles in the 4th.
The rule is " Every consecutive line has a number that is one less than twice the previous line ".
How many marbles are there in 6th line ?
In 1st line , 2 marbles are there.
In 2nd line, (2×2)-1 = 3 marbles are there.
In 3rd line, (2×3)-1 = 5 marbles are there.
In 4th line, (2×5)-1 = 9 marbles are there.
In 5th line, (2×9)-1 = 17 marbles are there.
In 6th line, (2×17)-1 = 33 marbles are there.
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