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下面这些题目,是我在CXD一本书里做的题目,有答案没解说,我在做的时候有些疑问,所以拿出来跟大家讨论, 有??的,说明我质疑标准答案. 请同学们帮忙一起解解题,也希望跟我一样存在难点的同学得到帮助, 谢谢~~~~~~~~ 1.Jerome wrote each of the integers 1 through 20,inclusive, on a separate index card. he placed the cards in a box, then drew cards one at a time randomly from the box, without returning the cards he had already drawn to the box. in order to ensure that the sum of all the cards he drew was even, how many cards did jerome have to draw? a.19, b.12, c,11, d,10, e,3 answer is B 2.during a sale at an office supply store, for every box of paper clips purchased for 15 cents, a second box can be purchased for 4 cents.how many boxes of paper clips did Paul buy if he spent 91 cents on boxes of paper clips? a. 6, b, 7, c,8, d,9, e,10. answer is d. 3.A box contains 100 balls, numbered from 1 to 100. If three balls are selected at random and with replacement fm the box, what is the probability that the sum of the three numbers on the balls selected fm the box wil be odd? a. 1/4, b.3/8, c.1/2 d,5/8, e.3/4 answer is c 4.the width of a rectangle is 6cm less than the length. if the perimeter of the rectangle is 48cm, what is the length of the rectangle in the centimeters? a. 48, b.15, c.12, d,9 e.6 answer is b. ( ????) 5.together, andrea and brian weigh P pounds, Brian weighs 10 pounds more than Andrea. Brian and Andrea's dog, Cubby, weighs p/4 pounds more than Andrea. In terms of P.What is Cubby's weight in pounds? a.P/2-10, b.3p/4-5 c3p/2-5 d 5p/4-10 e.5p-5 answer is b (????) 6.a painter has painted one-third of a rectangular wall which is ten feet high. when she has painted another 75 square feet of wall, she will be three-quarters finished with the job. what is the length ( the horizontal dimension) of the wall? a. 18 feet b.12feet c 10feet d.9 feet e.6 feet. answer is A
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