15 POINTS AND A BRAINLIEST TO THE CORRECT ANSWER!!! PLS HELP ASAP
A security alarm requires a four-digit code. The code can use the digits 0–9 and the digits cannot be repeated.

Which expression can be used to determine the probability of the alarm code beginning with a number greater than 7?

A) (2P1)(9P3)/10P4

B) (2C1)(9C3)/10C4

C)(10P1)(9P3)/10P4

D)(10C1)(9C3)/10C4

Question

20-04-2017
Mathematics

contestada

15 POINTS AND A BRAINLIEST TO THE CORRECT ANSWER!!! PLS HELP ASAP
A security alarm requires a four-digit code. The code can use the digits 0–9 and the digits cannot be repeated.

Which expression can be used to determine the probability of the alarm code beginning with a number greater than 7?

A) (2P1)(9P3)/10P4

B) (2C1)(9C3)/10C4

C)(10P1)(9P3)/10P4

D)(10C1)(9C3)/10C4

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bcalle bcalle · Answer 1 · 2017-04-20T18:51:10+02:00

I believe it is LETTER A.
There are 4 spots to be filled and the order matters. When order matters you have to use Permutations (P).
The first spot has a requirement that the number has to be greater than 7. There are only 2 numbers in the set that are greater than 7, 8 & 9.
So for spot 1 you have 2P1.
You have 4 remaining spots to fill and the order still matters so it will be another permutation. Since you cannot use repeats, we only have 9 numbers left to choose from and we are going to fill the 3 slots with these 9 numbers. 9P3
Only choice A has these options