How many phone numbers are possible if you already have the area code (xxx-xxxx) if no zero is allowed in the first position?
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3What do you think? – barak manos Aug 03 '16 at 20:19
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I don't even know the first step or what the formula would be – Jennifer Aug 03 '16 at 20:23
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Hint:
You have $7$ slots. In the first one, the only possible choices are $1-9$. In the last 6, the choices are $0-9$ for each slot.
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