How many 6-digit numbers can be formed using the digits 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9 if the first digit cannot be 0? Repeated digits are allowed.
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Using the fundamental counting principle / basic principle of counting
we have 9 possible choices for the first digit
and 10 possible choices for the last 5 digits
so the possible combinations are
9 * 10 * 10 * 10 * 10 * 10 = 900000 possible combinations
we have 9 possible choices for the first digit
and 10 possible choices for the last 5 digits
so the possible combinations are
9 * 10 * 10 * 10 * 10 * 10 = 900000 possible combinations
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9*10^5. ///