【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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1 o: }3 x3 B4 j  c! ~Read 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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正确答案:A
5 B) ^1 A( r1 E( u5 O/ Y, m& n; o
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" v! d! {6 c& _* Q% P- L& d; lThe 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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