What will come in place of the question mark(?) in the following number series
7 10.5 21 52.5 157.5 ?

Options

A. 451.25
B. 551.25
C. 651.25
D. 556

Answer

To solve the number series: 7, 10.5, 21, 52.5, 157.5, ?, we need to identify the pattern in the series.

### Step 1: Identify the pattern
Let's look at how each number relates to the next one in the series.

- From 7 to 10.5:
\[ 7 \times 1.5 = 10.5 \]

- From 10.5 to 21:
\[ 10.5 \times 2 = 21 \]

- From 21 to 52.5:
\[ 21 \times 2.5 = 52.5 \]

- From 52.5 to 157.5:
\[ 52.5 \times 3 = 157.5 \]

### Step 2: Continuing the pattern
Now we can see that the multipliers are increasing by 0.5 each time: 1.5, 2, 2.5, 3.

The next multiplier in the pattern will be:
\[ 3 + 0.5 = 3.5 \]

### Step 3: Calculate the next number
Now, we will multiply the last number in the series (157.5) by 3.5:
\[ 157.5 \times 3.5 = 551.25 \]

### Conclusion
Thus, the number that will come in place of the question mark (?) is:
\[ \boxed{551.25} \]