What will come in place of question mark (?) in the given number series questions?
1.5 2.5 7 24 100 ?

Options

A. 505
B. 210
C. 570
D. 310

Answer

To find the missing number in the series 1.5, 2.5, 7, 24, 100, ?, we can observe the pattern in how each number is derived from the previous one.

### Step-by-Step Solution:

1. **Identify the first two numbers:**
- The first number is 1.5 and the second number is 2.5.
- To get from 1.5 to 2.5, we can multiply 1.5 by 1 and then add 1:
\[ 1.5 \times 1 + 1 = 1.5 + 1 = 2.5 \]

2. **Identify the next two numbers:**
- The second number is 2.5 and the third number is 7.
- To get from 2.5 to 7, we multiply 2.5 by 2 and then add 2:
\[ 2.5 \times 2 + 2 = 5 + 2 = 7 \]

3. **Continue with the next pair:**
- The third number is 7 and the fourth number is 24.
- To get from 7 to 24, we multiply 7 by 3 and then add 3:
\[ 7 \times 3 + 3 = 21 + 3 = 24 \]

4. **Proceed to the next pair:**
- The fourth number is 24 and the fifth number is 100.
- To get from 24 to 100, we multiply 24 by 4 and then add 4:
\[ 24 \times 4 + 4 = 96 + 4 = 100 \]

5. **Find the missing number:**
- Now we need to find the number that comes after 100.
- We multiply 100 by 5 and then add 5:
\[ 100 \times 5 + 5 = 500 + 5 = 505 \]

Thus, the missing number in the series is **505**.