What percentage of numbers from 1 to 70 have 1 or 9 in the unit's digit?

Given Data

• Range of integers: 1 to 70 (inclusive)
• We need the percentage of numbers whose unit digit is 1 or 9

Key Idea

In every block of 10 consecutive integers (e.g., 1–10, 11–20, …), the unit digits cycle through 0–9 exactly once. Therefore, in each block of 10 numbers, exactly two numbers end with 1 and 9.

Step-by-Step
Total blocks of 10 between 1 and 70 = 7 blocks (1–10, 11–20, …, 61–70)Count with unit digit 1 or 9 per block = 2Total such numbers = 7 × 2 = 14Total numbers overall = 70Percentage = (14 ÷ 70) × 100 = 20%

Common Pitfalls

• Forgetting that 70 is included; the last block is 61–70 and still contains 61 and 69.
• Counting per 10 but then not scaling the count across all 7 blocks.

Final Answer
Required percentage = 20%.