每日一题

Mathematics>Standard Multiple Choice

Read the following SAT test question and then click on a button to select your answer.

Add 8x to 2x and then subtract 5 from the sum. If x is a positive integer, the result must be an integer multiple of

(A) 2
(B) 5
(C) 8
(D) 10
(E) 15

答案和解析

答案：B

解析：

The mathematical expression given in the question is (8x) + (2x)-5, which is equivalent to (10x)-5. The expression (10x)-5 can be factored as 5((2x)-1). For every positive integer x, 5((2x)-1) must be a multiple of 5. If x = 1, then 5((2x)-1) = 5, which is not an integer multiple of 2, 8, 10, or 15. Therefore, the correct answer is 5.