The probability of choosing a 6 at random from a standard deck of playing cards is 1/13.

1/13 chance, because it's one, out of the 13 cards, so 1/13

1/13 beacause there are 13 cards in the deck and thats just one of them

The plan is 100 songs downloaded equally on each week for 5 weeks, so,

100 songs/ 5 weeks; 20 songs per week.

Number of Weeks (x)              Songs left to download (y)
            1                                                  100
            2                                                  80
            3                                                  60
            4                                                  40
            5                                                  20 

The rate of change is 20 songs per week. 

y = mx + b, input in the STAT feature of the calculator.

m = -20
b = 120