It's an arithmetic progression with first term = 8 and common difference d =2:
so the next term is 14 + 2 = 16
The common number is 6.
72/6=12
60/6=10
12/10
simplify that, it is 6/5
For the first digit there are 7 choices. For the second digit there are 6 choices (because we can't use the same one again). And so on, until there is only one choice for the last digit.
The number of possible codes is this:
7*6*5*4*3*2*1 = 7! = 5040
Convert 20% to a decimal by dividing by 100, = 0.20
16,000 x 0.20 = 3,200 deposit she paid. Subtract that from the total cost
16,000- 3,200= 12,800
