Math
posted by John on .
ok we got this packet that has an answer key and we g0tta show our work of how to get the answer. okayyy... they all seem like really easy problems s0 i think im just dumbbb
"a bag has 6 red and 2 white marbles. If two marbles are selected, what is the probability that one is red and the other is white?"  the answer is 3/7. how do i get that??
it seems like a real easy problem, i know. but i cant seem to get it :
next. "Jose has 5 dimes, 7 nickels, and 4 pennies in his pocket. he selects 4 coins. What is the probability that he has 2 dimes and 2 pennies." answer is 3/91.
Last one. "If a card is selected from a deck of cards, find the probability that it is not red or not a face card." answer is 23/26. This one really doesnt make sense ???

first one:
C(6,1)*C(2,1)/C8,2) = 6*2/28 = 3/7
second one:
C(5,2)*C(4,2)/C(16,4) = 10*6/1820 = 3/91
third one:
the key word is the "or"
prob(not red OR not a facecard)
= Prob(not red) + prob(not a facecard)  prob(not red AND not a facecard)
= 26/52 + 40/52  20/52
= 46/52
= 23/28 
thank you so much!