prep 数学一道，求解，谢谢

carolcai

In a certain deck of cards, each card has a positive integer written on it.  In a multiplication game, a child draws a card and multiplies the integer on the card by the next larger integer.  If each possible product is between 15 and 200, then the least and greatest integers on the cards could be

 

(A) 3 and 15

(B) 3 and 20

(C) 4 and 13

(D) 4 and 14

(E) 5 and 14

我选的D，14不可以在这里面吗？答案是C。求牛牛们解惑啊~

In a certain deck of cards, each card has a positive integer written on it.  In a multiplication game, a child draws a card and multiplies the integer on the card by the next larger integer.  If each possible product is between 15 and 200, then the least and greatest integers on the cards could be

 

(A) 3 and 15

(B) 3 and 20

(C) 4 and 13

(D) 4 and 14

(E) 5 and 14

我选的D，14不可以在这里面吗？答案是C。求牛牛们解惑啊~

shiverson

这题算是有trick吧

相乘，但必须后面数比前面数大才能乘

所以最小，4*5＝20    最大13*14＝182

14可以在答案里，但它是大数，必须第一张是13，否则超了

carolcai

哦，感谢shiverson,帮我解了好几题