Question : Directions: In the following question a series is given, with one number missing. Choose the correct alternative from the given ones that will complete the series.
1, 6, 15, ?, 45, 66
Option 1: 26
Option 2: 24
Option 3: 28
Option 4: 23
Correct Answer: 28
Solution :
Given:
1, 6, 15, ?, 45, 66
Add the numbers with the difference of 4 to the previous term to obtain the next term.
1 + 5 = 6;
6 + (5 + 4) = 6 + 9 = 15;
15 + (9 + 4) = 15 + 13 = 28;
28 + (13 + 4) = 28 + 17 = 45;
45 + (17 + 4) = 45 + 21 = 66
So, 28 is the missing number in the given series. Hence, the third option is correct.
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