经验教程|AMC8 -- 1990年真题解析
_原题为 AMC8 -- 1990年真题解析
Problem 1
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Answer: C
Solution:
One is 468, the other is 579. 468+579=1047.Problem 2
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Answer: A
Solution:
When dealing with positive decimals, the leftmost digits affect the change in value more. Thus, to get the largest number, we change the 1 to a 9.Problem 3
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Answer: E
Solution:
Reflecting the square across the diagonal drawn, we see that the shaded region covers exactly the unshaded region in the original square, and thus makes up 1/2 of the square .Problem 4
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Answer: E
Solution:
For integers, only the units digit affects the units digit of the final result, so we only need to test the squares of the integers from 0 through 9 inclusive. Testing shows that 8 is unachievable, so the answer is E.Problem 5
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Answer: B
Solution:
Clearly, 0.4<0.48017<0.5; 0.5*0.5*0.5=0.125, so B is the answer.
Since 0.48017 is quite close to 0.5, we can look for the answer choice that is just below 0.5*0.5*0.5=0.125 , which would be B .Problem 6
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Answer: D
Solution:
The options given in choices A, B, and E don't change the initial value (13579) much, the option in choice C decreases 13579 by a lot, and the one given in choice D increases 13579 by a lot.Problem 7
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Answer: C
Solution:
First we try for a positive product, meaning we either pick three positive numbers or one positive number and two negative numbers. It is clearly impossible to pick three positive numbers. If we try the second case, we want to pick the numbers with the largest absolute values, so we choose 5, -3, and -2. Their product is 30.Problem 8
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Answer: D
Solution:
After the price reduction, the sale price is 80*(1-0.25)=60 dollars. The tax makes the final price 60*1.1=66 dollars.Problem 9
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Answer: D
Solution:
We just count to find that there are 5 students in the C range.
There are 15 total, so the percentage is 5/15=33.3%.Problem 10
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Answer: A
Solution:
Let the date behind c be x. Now the date behind A is x+1, and after looking at the calendar, the date behind B is x+13. Now we have x+1+x+13=x+y. for some date y, and we desire for y to be x+14. Now we find that y is the date behind P.Problem 11
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Answer: E
Solution:
The only possibilities for the numbers are 11,12,13,14,15,16or10,11,12,13,14,15..
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