What percentage of numbers from 1 to 80 have 1 or 9 in the units digit?

Options

A. 0.01
B. 0.2
C. 0.21
D. 0.14

Answer

To solve the problem of finding what percentage of numbers from 1 to 80 have 1 or 9 in the units digit, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Range**:
We need to consider all numbers from 1 to 80. The total count of numbers in this range is 80.

2. **Count Numbers with 1 in the Units Digit**:
The numbers from 1 to 80 that have 1 in the units digit are:
- 1, 11, 21, 31, 41, 51, 61, 71
This gives us a total of **8 numbers**.

3. **Count Numbers with 9 in the Units Digit**:
The numbers from 1 to 80 that have 9 in the units digit are:
- 9, 19, 29, 39, 49, 59, 69, 79
This also gives us a total of **8 numbers**.

4. **Calculate the Total Numbers with 1 or 9 in the Units Digit**:
Adding the counts from steps 2 and 3:
- Total = 8 (for 1) + 8 (for 9) = **16 numbers**.

5. **Calculate the Percentage**:
To find the percentage of numbers from 1 to 80 that have 1 or 9 in the units digit, we use the formula:
\[ \text{Percentage} = \left( \frac{\text{Number of favorable outcomes}}{\text{Total outcomes}} \right) \times 100 \]
Substituting the values:
\[ \text{Percentage} = \left( \frac{16}{80} \right) \times 100 = 20\% \]

### Final Answer:
The percentage of numbers from 1 to 80 that have 1 or 9 in the units digit is **20%**.