61, 66, 70, 71, 76, ? , 81, 86, 70, 91

Options

A. 70
B. 71
C. 80
D. 96

Explanation

To find the missing number in the series: 61, 66, 70, 71, 76, ?, 81, 86, 70, 91, we can analyze the pattern of the numbers step by step.

### Step 1: Identify the series structure
The series appears to be alternating between two different patterns. We can separate the series into three distinct groups based on their positions:

- Group 1 (1st, 4th, 7th, 10th positions): 61, 71, 81, 91
- Group 2 (2nd, 5th, 8th positions): 66, 76, 86
- Group 3 (3rd, 6th, 9th positions): 70, ?, 70

### Step 2: Analyze Group 1
In Group 1, the numbers are:
- 61 (1st term)
- 71 (4th term)
- 81 (7th term)
- 91 (10th term)

We can see that each number increases by 10:
- 61 + 10 = 71
- 71 + 10 = 81
- 81 + 10 = 91

### Step 3: Analyze Group 2
In Group 2, the numbers are:
- 66 (2nd term)
- 76 (5th term)
- 86 (8th term)

Again, we see that each number increases by 10:
- 66 + 10 = 76
- 76 + 10 = 86

### Step 4: Analyze Group 3
In Group 3, the numbers are:
- 70 (3rd term)
- ? (6th term)
- 70 (9th term)

Here, we notice that the number 70 is repeated in the 3rd and 9th positions. Since it is a repeating number, it is logical to assume that the missing number in the 6th position should also be 70.

### Conclusion
Thus, the missing number in the series is **70**.

### Final Answer
The missing number is **70**.

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