a lock has a 4 digit combination where no number can be repeated how many possible combinations are there​

4,536

Step-by-step explanation:

Ok so lets write down any old 4 digit number

abcd

How many choices do we have for the digit a? We have 9 choices (since the first digit cannot be 0). Now for each possible choice of a we have 9 choices for b (since we want b to be a different digit to a and we now allow 0).

So for choice of the ab part we have 9∗9=81 possibilities.

Now for each of these we have 8 choices for c (to avoid c being the same as either a or b). And for each of these we have 7 choices for d (to avoid d being the same as either a,b or c).

So in total there are 9∗9∗8∗7=4536 possible numbers.

total amount of money that he should pay if he has not used his duty free exemption is $98

step-by-step explanation:

given a united states citizen returning to the states declares the following items at the customs office: 3 shirts at $8.50 each 2 dresses at $27.50 each 1 pair of gold cuff links at $17.50 per pair. we have to find how much he pay

cost of 3 shirts if one cost at $8.50 is

cost of 2 dresses if one cost at $27.50 is  

cost of 1 pair of gold cuff at $17.50

so, total amount of money that he should pay if he has not used his duty free exemption is   $25.5+$55+$17.50=$98