27, 98, 36, 89, 45, ?

Options

A. 78
B. 79
C. 80
D. 81

Explanation

To find the missing number in the series: 27, 98, 36, 89, 45, ?, we can analyze the pattern in the series step by step.

### Step 1: Identify the pattern
The series alternates between two sequences:
- The first sequence consists of the numbers in the odd positions: 27, 36, 45
- The second sequence consists of the numbers in the even positions: 98, 89, ?

### Step 2: Analyze the first sequence
The first sequence is: 27, 36, 45.
- The difference between 27 and 36 is 9 (36 - 27 = 9).
- The difference between 36 and 45 is also 9 (45 - 36 = 9).
- Therefore, we can conclude that the first sequence increases by 9 each time.

### Step 3: Analyze the second sequence
The second sequence is: 98, 89, ?.
- The difference between 98 and 89 is -9 (89 - 98 = -9).
- This indicates that the second sequence decreases by 9 each time.

### Step 4: Calculate the missing number
To find the missing number in the second sequence, we subtract 9 from the last known number (89):
- 89 - 9 = 80.

### Conclusion
The missing number in the series is **80**.