There are 20,000 different phone numbers possible that is 7-digits long and start with either 824 or 825.
Fundamental Principle of Counting, also called the counting rule, is the method to count how many ways multiple independent events can occur.
Based on the given information, all phone numbers are 7-digits long and starts with either 824 or 825. Hence, the four last digits will be the combination of numbers from 0 to 9.
Thus, by Fundamental Principle of Counting, the number of possible outcomes is 20,000.
= (number of phone numbers starting with 824) + (number of phone numbers starting with 825)
= (10 x 10 x 10 x 10) + (10 x 10 x 10 x 10)
= 20,000
Learn more about counting principle here: brainly.com/question/16050707
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