[求助]幾道數學題

Claire · 发表于 2004-2-14 12:01:00

禮拜一考試，緊急求助

1 on a certain road, 10% of the motorists exceed the posted speed limit and receive speeding tickets,but 20% of the motorists exceed the posted speed limit do not receive speeding tickets, what percent of the motorists on that road exceed the posted speed limit

a 10.5% b 12.5% c 15% d 22% e 30%

the above key is b,why not e?

2 in sequence Q, the first number is 1/2, and each subsequent number is the sequence is determined by doubling the previous number and hen adding 2, how many times does the unit digit 8 appear in the first 15 numbers of the sequence?

a 7 b 8 c 10 d 12 e 13

the above key is e,ask for explanation

thanks

terp · 发表于 2004-2-14 15:08:00

1. Suppose there are total 100 motorists. So there are 10 motorists who exceed the posted speed limit and receive speeding tickets. You know these 10 motorists are 80% of the motorists exceed the posted speed limit do not receive speeding tickets. So there are 10/0.8=12.5 motorists exceeding the limits. So the answer is 12.5%.

terp · 发表于 2004-2-14 15:13:00

2. The sequence will be 1/2, 3, 8, 18,...... then you will see the rest of the sequence are all having a unit digit 8 because the unit digit of (8*2+2). So only the first 2 elements of the sequence are not with unit digit 8. Then the answer is 15-2=13

Claire · 发表于 2004-2-14 16:30:00

i am so careless that i treated "double" as "square",thanx for the explanation

terp · 发表于 2004-2-15 02:10:00

When you deal with quantitative, paying attention to the details and exception is very important. After all, they are not hard.

[求助]幾道數學題

[求助]幾道數學題

所属分类: GMAT考试

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