2017年小升初英语奥数题练习（3）

　　1. An ant covers a distance of 90 meters in 3 hours. The average speed of the ant in decimeters per minute is ____.

　　2. Of the 28 T-shirts in a drawer， six are red， five are blue， and the rest are white. If Bob selects T-shirts at random whilst packing for a holiday， what is the least number he must remove from the drawer to be sure that he has three T–shirts of the same color?

　　3. Did you know? In the decimal number system (base 10) ten different digits， 0 to 9， are used to write all the numbers. In the binary number system (base 2) two different digits are used， i.e. 0 and 1.

　　Which one of the following numbers is not a valid number in the octal number system (base 8)?

　　A.128 B. 127 C.126 D.125 E.124

　　4. Three girls A， B and C run in a 100 m race. When A finishes， B is 10 m behind A and when B finishes C is 20 m behind B. How far in meters was C from A when A finished? (Let’s assume all the athletes run at a constant speed)

　　参考答案

　　1. 单位换算，注意单词，90×10÷（3×60）＝5。

　　2. 利用抽屉原理可得出结果为7。

　　3. A 考察我们学过的简单的进制问题，显然8进制中没有8出现。

　　4. 28米，根据距离比求出速度比，三者的速度比为1：9/12：18/25。