Random digits 0,1,2,3,4,5,6,7,8,9. what is the probability that a multiple of 4 is picked?

Joseph haydn pet store offers wide variety of leashes for dogs. the store purchases one popular type of leash from its manufacturer for $4.38 each. joseph haydn pets marks up leashes at a rate of 238% of cost. what is the retail price of the popular leash?

How do you solving the solution of each system using elimination?

Can someone me with #s 8, 9, and 11. with just one of the three also works. prove using only trig identities.