Understanding the Number Series Pattern

The question presents a sequence of numbers: 15, 45, 75, 105, ?. We need to find the next number in this series.

Let's analyze the relationship between consecutive numbers in the series:

• The first term is 15.
• The second term is 45.
• The third term is 75.
• The fourth term is 105.

To find the pattern, we calculate the difference between each pair of consecutive terms:

• Difference between the second and first term:
  
  $45 - 15 = 30$
• Difference between the third and second term:
  
  $75 - 45 = 30$
• Difference between the fourth and third term:
  
  $105 - 75 = 30$

We observe a constant difference of 30 between consecutive terms. This indicates that the series is an arithmetic progression.

Calculating the Missing Number

Since the series follows an arithmetic progression with a common difference of 30, we can find the next term (the one replacing the question mark) by adding the common difference to the last known term.

The last known term is 105.

The common difference is 30.

Therefore, the missing number is:

So, the number that replaces the question mark (?) is 135.

Summary Table