2012年04月06日
考试类型: Mathematics > Standard Multiple Choice
Read the following SAT test question and then click on a button to select your answer.
A machine can insert letters in envelopes at the rate of 
per minute. Another machine can stamp the envelopes at the rate of per 
second. How many such stamping machines are needed to keep up with 
inserting machines of this kind?
A.
B.
C.
D.
E.
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正确答案:A 解析: First you can change Let
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minute to 
seconds so that the ratios are both in envelopes per second. One inserting machine inserts letters at the rate of 
per 
seconds, or 
per second. So 
machines would insert 
letters per second.
be the number of stamping machines needed to keep up with 
inserting machines. Then, since one machine stamps 
envelopes per second, 
machines stamp 
envelopes per second. You can write the equation 
, which gives 
.