# Math Challenge - Find a Missing Counting Number in a Sequence

Let’s solve this problem. Here is a Sequence, Choose the right answer to complete the series of this Math Challenge.

25, 35, 45, ____, 65, 75.

Before solving learn the steps of how to solve it,

**Rules or septs to find the missing number in a sequence**

To find a missing counting number in a sequence, we need to follow these steps:

**Step 1:** Determine the order of the sequence.

The first step is to determine the order of the counting numbers in the sequence. The sequence can be in ascending order or descending order. Ascending order means the numbers increase in value from left to right, and descending order means the numbers decrease in value from left to right.

**Step 2:** Find the difference between the numbers.

Once we know the order of the sequence, we need to find the difference between the numbers that are next to each other. For example, if the sequence is 2, 4, 6, 8, 10, we would find the difference between each number as follows:

4 - 2 = 2 6 - 4 = 2 8 - 6 = 2 10 - 8 = 2

In this case, the difference between each number is 2.

**Step 3:** Use the difference to find the missing number.

Now that we know the difference between the numbers, we can use this information to find the missing number. If the sequence is in ascending order, we add the difference to the last number in the sequence to find the missing number. If the sequence is in descending order, we subtract the difference from the last number in the sequence to find the missing number.

**For example,** if the sequence is 2, 4, 6, ___, 10 and we know the difference between each number is 2, we can use the following formulas to find the missing number:

**Ascending order**: Last number in sequence + difference 10 + 2 = 12

Therefore, the missing number is 8, and the sequence becomes 2, 4, 6, 8, 10.

**Descending order:** Last number in sequence - difference 6 - 2 = 4

Therefore, the missing number is 4, and the sequence becomes 2, 4, 6, 4, 10.

By following these steps, we can easily find the missing counting number in a sequence.

- A. 15
- B. 40
- C. 55
- D. 85

C. 55

**Answer:** The missing number is **55**.

**Explanation:**

We can observe that each number in the sequence is increasing by 10. Therefore, to find the missing number, we need to add 10 to the previous number, which is 45.

45 + 10 = 55

Hence, the missing number in the sequence is 55.

Therefore, the answer is option C. 55