Q1. 

答案：C 镜面反射

Q2. 

答案：E 其他选项的图案，里外形状都一样的

 

Q3.

答案：C 选项A是90度逆时针旋转；选项B中，灰色三角没有变化；选项D中，箭头没有变化

Q1. Jo's collection contains US, Indian and British stamps. If the ratio of US to Indian stamps is 5 to 2 and the ratio of Indian to British stamps is 5 to 1, what is the ratio of US to British stamps?

　　A. 5 : 1

　　B. 10 : 5

　　C. 15 : 2

　　D. 20 : 2

　　E. 25 : 2

　　Correct Answer: E

　　Explanation:

Indian stamps are common to both ratios. Multiply both ratios by factors such that the Indian stamps are represented by the same number. US : Indian = 5 : 2, and Indian : British = 5 : 1. Multiply the first by 5, and the second by 2.

 

Now US : Indian = 25 : 10, and Indian : British = 10 : 2 Hence the two ratios can be combined and US : British = 25 : 2

 

Q2. A 3 by 4 rectangle is inscribed in circle. What is the circumference of the circle?

　　A. 2.5π

　　B. 3π

　　C. 5π

　　D. 4π

　　E. 10π

　　Correct Answer: C

　　Explanation:

Draw the diagram. The diagonal of the rectangle is the diameter of the circle. The diagonal is the hypotenuse of a 3,4,5 triangle, and is therefore, 5. Circumference = π.diameter = 5π