Analysis: the probability of the first even number is 2/5, the second even number is 3/5, and the probability of simultaneous satisfaction is 2/5*3/5=6/25.
5. The interactive link of "Treasure Box" in CCTV's "Lucky 52" column is a quiz game, and the rules of the game are as follows: among the 20 trademark cards, the back of 5 trademark cards is marked with a certain bonus amount, and the back of other trademarks is a crying face. If you turn to crying, you won't get the prize, and the audience participating in this game will have three chances to flop (the turned cards can't be flipped again). A spectator has won several prizes in the first two flips, so the probability of winning the third flop is (c)
Analysis: There are 18 unknown trademarks left in the last flop, and three of them have bonuses, so the winning probability is 1/6.
6. From 100 cards with numbers from 1 to 100, randomly draw a card, and the probability of its number being a multiple of 3 is (A) A, 33/ 100b, 34/ 100 C.
Analysis: The multiple of 3 in the integer from 1 to 100 is only: 1 times 3 = 2 times 3 = 33 times 6, ... 3 = 99 * * 33, so the answer is A.
7. After washing a playing card (52 cards except Wang), draw two cards in a row. The probability that the first card is a heart and the second card is a spade is (a).
a、 13/52 B、 1/ 17 C、 13/204 D、 1/ 16
Analysis: Because the two cards are drawn successively (simultaneously) instead of sequentially, the probability is 13/52 instead of 13/5 1.
8. In order to estimate the number of antelope in a certain area, 20 antelope were captured, marked and put back. After the marked antelope was completely mixed with the antelope, 40 antelopes were captured for the second time, and two of them were found to be marked. So it is estimated that this area has antelope (b).
200 B 400 C800 D 1000
Analysis: It can be inferred from "40 yellow sheep were caught for the second time after the marked yellow sheep and the yellow sheep were completely mixed, and two of them were found to be marked" that 20 marked sheep accounted for 2/40 of the total number of sheep, that is, 1/20 = 400.