6. Each telephone number in a city consists of 7 digits. а. How many telephone numbers are possible if every number must start with the digit 7 ? b. How many telephone numbers start with 3 and contain the digit 6 at least once? c. How many telephone numbers have no repeated digits but must end with an odd digit?

Advanced Engineering Mathematics
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ISBN:9780470458365
Author:Erwin Kreyszig
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Under permutation and combination topic
6. Each telephone number in a city consists of 7 digits.
а.
How many telephone numbers are possible if every number must start
with the digit 7 ?
b.
How many telephone numbers start with 3 and contain the digit 6 at
least once?
С.
How many telephone numbers have no repeated digits but must end
with an odd digit?
7. There are 7 boys and 5 girls in a class.
а.
How many ways can a committee of 4 people be selected if there must
be 2 boys and 2 girls on the committee?
b.
How many ways can this committee of 4 people be selected if there must
be at least 2 girls on the committee?
Transcribed Image Text:6. Each telephone number in a city consists of 7 digits. а. How many telephone numbers are possible if every number must start with the digit 7 ? b. How many telephone numbers start with 3 and contain the digit 6 at least once? С. How many telephone numbers have no repeated digits but must end with an odd digit? 7. There are 7 boys and 5 girls in a class. а. How many ways can a committee of 4 people be selected if there must be 2 boys and 2 girls on the committee? b. How many ways can this committee of 4 people be selected if there must be at least 2 girls on the committee?
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