Question

If a card is chosen from a standard deck of cards, what is the probability of getting a five or a seven?
4/52
1/26
8/52
1/169

If two cards are chosen from a standard deck of cards, what is the probability of getting a five followed by a seven? (assume replacement of the first card)
1/13 * 1/13
1/13 * 1/12
1/13 + 1/13
¼ + ¼

explain replacement of first card? thx

Answer 1

There are 4 fives and 4 sevens, so we are interested in 8 specific cards
prob(5 or 7) = 8/52 = 2/13
(they should reduce their answers to lowest term fractions)

Prob(5, then a 7) = (4/52)(4/52) = 1/169
(oh, now they reduce the fractions to lowest terms, love the consistency)