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20 13 Haidian midterm mathematics
1.The difference between A and B is 45, and the ratio of A and B is 5:2. What are they?

A =5*45/(5-2)=75,B =2*45/(5-2)=30。

2. A square with a side length of12.56m can be enclosed by a line. If this line forms a circle, what is the area of the circle?

π*(4* 12.56/2π)? = 63 1.0 144/π≈200.96 m2

At present, the price of crude oil in the international market is about $78 per barrel, which is about one year higher than a year ago. What was the price of a barrel of crude oil a year ago?

How much more than a year ago?

Three students, A, B and C, all like collecting stamps. A has 18 stamps, which is equivalent to three-quarters of B. The ratio of C stamps to B stamps is exactly 2:3. Who has the least stamps and how many?

A There are 18 stamps.

A has 18 stamps, which is equivalent to three-quarters of B, so B has 18 divided by three-quarters equals 24 stamps.

The ratio of the number of stamps in C to that in B is exactly 2:3, and C has 24*2/3= 16.

Therefore, C stamps are the least, 16.