Question

You are setting up a system of programming codes for a universal TV remote. Each code will have five digits and cannot include a 0 or repeat any digits. How many codes:
A) do not contain a 1?
My answer: 8x7x6x5x4 = 6720 codes

B)have 2 as the 2nd digit and 4 as the fourth digit?
- I don't know how to do this one

C)begin with an even number
My answer: 4x8x7x6x5 = 6720

D) begin and end with an even number
My answer: 4x3x8x7x6 = 4032

Are my answers correct... And how do I do B)

Answer 1

A - correct

B - I assume we can now use the 1
?2?4? , so we can use only 7 other digits
number of ways
= 7x1x6x1x5 = 210

c - correct

D - evens at front and end
4x?x?x?x3 , leaves 7 for the other places= 4x7x6x5x3 = 2520

Answer 2

A - correct
B - I assume we can now use the 1?2?4? , so we can use only 7 other digitsnumber of ways= 7x1x6x1x5 = 210
c - correct
D - evens at front and end4x?x?x?x3 , leaves 7 for the other places= 4x7x6x5x3 = 2520
also the other person stole my answer