Question by Cloud - Discuss with MathYouLike

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12/12/2017 at 16:38

The numbers 2 through 9 on a telephone keypad, like the one shown, are associated with the letters of the alphabet. Each person in a particular office is assigned a phone extension based on the first three letters of his or her last name. For instance, John DOE has the extension 363, and Marvella JOHnson has the extension 564. How many unique three-digit extensions can be assigned using the digits 2 through 9?
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Lê Quốc Trần Anh Coordinator 13/12/2017 at 16:36

In each hundreds from 222 - 999, there are \(299-222+1=78\left(extensions\right)\)/each hundreds

From 222 - 999 there are: \(9-2+1=8\left(hundreds\right)\)

So there are: \(78\cdot8=624\) unique three-digit extensions can be assigned.
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KEITA FC 8C 19/12/2017 at 12:49

In each hundreds from 222 - 999, there are 299−222+1=78(extensions)299−222+1=78(extensions)/each hundreds

From 222 - 999 there are: 9−2+1=8(hundreds)9−2+1=8(hundreds)

So there are: 78⋅8=62478⋅8=624 unique three-digit extensions can be assigned.

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