Question

In the following series, find which of the given numbers is wrong and does not follow the pattern:
21 105 525 2615 13125 65625

• A. 13125
• B. 525
• C. 65625
• D. 2615
• E. 105

Hint:

In a multiplication series, look at the last digit. Since $5 \times 5 = 25$, every term after 105 must end in 5 or 25.

Answer 1

The Correct Option is D

Concept: Identify the multiplier or constant difference between consecutive terms.
Step 1: Check the relationship between first two terms.
$21 \times 5 = 105$.

Step 2: Apply the pattern to subsequent terms.
• $105 \times 5 = 525$ (Correct)
• $525 \times 5 = 2625$ (But the series gives 2615)

Step 3: Verify if 2625 maintains the rest of the series.
$2625 \times 5 = 13125$ (Matches the next term). $13125 \times 5 = 65625$ (Matches the final term). Therefore, 2615 is the wrong number; it should be 2625.