WAEC - Further Mathematics (2020 - No. 31)
Explanation
To find the number of three-digit odd numbers less than 500 that can be formed using the digits 1, 2, 3, 4, and 5 with repetition allowed, we follow these steps:
Identify the conditions:
Three-digit number: The number must have three digits.
Odd number: The last digit must be odd.
Less than 500: The first digit must be less than 5.
Choose the last digit:
The last digit (which determines if the number is odd) can be one of the odd digits: 1, 3, or 5. Thus, there are
\(3 \text{ options for the last digit.}\)
Choose the first digit:
The first digit must be less than 5. Therefore, it can be one of the digits: 1, 2, 3, or 4. Thus, there are
\(4 \text{ options for the first digit.}\)
Choose the middle digit.
The middle digit can be any of the digits: 1, 2, 3, 4, or 5 (since repetition is allowed). Thus, there are
\(5 \text{ options for the middle digit.}\)
Calculate the total combinations:
Now we multiply the number of choices for each digit:
\(\text{Total combinations} = (\text{options for first digit}) \times (\text{options for middle digit}) \times (\text{options for last digit})\)
\(\text{Total combinations} = 4 \times 5 \times 3 = 60\)
The number of three-digit odd numbers less than 500 that can be formed is 60.
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