The wrong number of the sequence 5, 15, 45, 135, 395, 1215, 3645 is

Options

A. 395
B. 135
C. 45
D. 5

Answer

To determine the wrong number in the sequence 5, 15, 45, 135, 395, 1215, 3645, we will analyze the pattern of the sequence step by step.

### Step 1: Identify the pattern
Let's examine the sequence: 5, 15, 45, 135, 395, 1215, 3645.

We can start by checking the ratios or the multiplication factors between consecutive terms.

### Step 2: Calculate the ratios
- From 5 to 15: \( 15 = 5 \times 3 \)
- From 15 to 45: \( 45 = 15 \times 3 \)
- From 45 to 135: \( 135 = 45 \times 3 \)

Now let's check the next term:
- From 135 to 395: \( 395 \neq 135 \times 3 \)

Calculating \( 135 \times 3 = 405 \), which is not equal to 395.

### Step 3: Check the next term
Now, let's check the term after 395:
- From 395 to 1215: \( 1215 = 395 \times 3.07 \) (approximately, not a clean multiplication)

### Step 4: Identify the wrong number
Since the multiplication factor from 135 to the next term should have been 3, but it resulted in 395 instead of 405, we can conclude that 395 is the wrong number in the sequence.

### Conclusion
The wrong number in the sequence is **395**.

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