If the following question, select the number which can be placed at the sign of question mark (?) from the given alternatives
4, 13, 16, 17, 28, 21, ?, 25, 52
Answer
Correct Answer : c ) 40
Explanation :In the given question,
4, 13, 16, 17, 28, 21, ?, 25, 52
let's look at 1st, 3rd, 5th, 7th and 9th term
4, 16, 28, ?, 52
these terms are in arithmetic progression with a common difference of 12.
4 + 12 = 16
16 + 12 = 28
28 + 12 = 40 (?)
40 + 12 = 52
also, we can observe that 2nd, 4th, 6th and 8th terms are in arithmetic progression with a common difference of 4.
13 + 4 = 17
14 + 4 = 21
21 + 4 = 25
Hence, (c) is the correct answer.
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