A gasoline tank on a certain tractor holds 16 gallons of gasoline. If the tractor requires 7 gallons to plow 3 acres, how many acres can the tractor plow with a tankful of gasoline?
(A) 6 and (6 over 7)
(B) 7 and (1 over 6)
(C) 7 and (1 over 3)
(D) 10 and (2 over 3)
(E) 37 and (1 over 3)
解释：
Think of setting up this problem as a ratio of the form “a is to b as c is to d,” which is mathematically equivalent to a over b = c over d. If 7 gallons of gasoline can plow 3 acres, then a over b is 7 over 3. Knowing that it represents the same proportion, what is c over d? Since there will only be one unknown variable, that variable can be solved for directly to find the answer.
In the question, you are told that 7 gallons of gasoline can plow 3 acres and you are asked to find how many acres, call itx, can be plowed by16 gallons. You can set up a ratio of the number of gallons of gasoline used to the number of acres plowed. Therefore, you have 7 over 3 = 16 over x. Cross-multiplying and solving forxgives you the answer of x = 48 over 7acres, or 6 and (6 over 7)acres.
正确答案是A。
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