# area and volume

The figure shows a concial object that is composed of a small right circular cone VAB and a frustum ACDB.The heights of the small circular cone and the frustum are 3m and 4m respectively

a.Find the ratio of the curved surface area of the small curved surface area of the small circular cone to that of the frustum

b.The curved surface of the small circular cone is now painted in purple,and that of the frustum is painted in green. If 2 cans of purple paint have been used to paint the cone,how many cans of green paint are required to paint the frustum?

a.9:40

b.80/9

### 2 個解答

• 最愛解答

(a) Add the small right circular cone VAB to a frustum ACDB. Then the big right circular cone VCD has height 3+4=7 cm.

So, the ratio of the curved surface area of the small circular cone to that of the big circular cone is 3^2 : 7^2 = 9 : 49.

Now the curved surface area of frustum ACDB is equal to curved surface area of big circular cone - curved surface area of small circular cone. So the ratio of curved surface area of the small circular cone to that of the frustum is 9 : (49-9) = 9 : 40

(b) 2 : ( cans of green paint for frustum) = 9 : 40

40 * 2 = 9(cans of green paint for frustum)

cans of green paint for frustum = 80/9

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