In following number series, two terms have been put within brackets. Choose the appropriate option

Look at this series: 3, 4, 7, 8, 11, 12, . . . What number should come next ?

** Option:**

**A.**7

**B.**10

**C.**14

**D.**15

**Answer: D . 15**

** Justification:**

This alternating addition series begins with 3;

then 1 is added to give 4;

then 3 is added to give 7;

then 1 is added, and so on.

Rule = (first number + 1) (second number + 3) (third number + 1) (fourth number + 3)...

Now The series is 3, 4, 7, 8, 11, 12...

(3 + 1 = 4), (4 + 3 = 7), (7 + 1 = 8), (8 + 3 = 11), (11 + 1 = 12) (12 + 3 = 15)...

So the answer is **d = 15.**