【SAT官方每日一题】22/8/12 Mathematics > Standard Multiple Choice

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Mathematics > Standard Multiple Choice

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. B5 U# q" v; c- R, s8 oRead the following SAT test question and then click on a button to select your answer.

For how many positive two-digit integers is the ones digit greater than twice the tens digit?

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B.

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D.

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% J. ?& f1 q* ~1 S' r/ c" c正确答案:A

4 Z# i! G5 z) ~) V/ ]1 [, m解析:
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The correct answer is (A). If the tens digit is 1, there are7  positive two-digit integers with the ones digit greater than twice the tens digit:
and 19. If the tens digit is 2 , there are 5  positive two-digit integers with the ones digit greater than twice the tens digit:  and 29. If the tens digit is 3 , there are 3 positive two-digit integers with the ones digit greater than twice the tens digit: and 39. If the tens digit is 4 , there is 4 positive two-digit integer with the ones digit greater than twice the tens digit:49 . If the tens digit is equal to or greater than 5, then the ones digits, which cannot be greater than  9 , is not greater than twice the tens digit. Therefore, there is a total of positive two-digit integers for which the ones digit is greater than twice the tens digit.

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