Page 84 - NUMINO Challenge_D2

Problem solving Key Points

1 A cylinder is made by revolving a rectangle with When the area of
an area of 8 cm2 around one side used as the the rectangle does
rotation axis. Find the minimum volume of the not change, the
cylinder. (The length and width of the rectangle volume of the
are whole numbers.) cylinder decreases
as the side length of
the rectangle that is
perpendicular to the
rotation axis
decreases.

2 A rectangle has a length that is twice as long as its To find the ratio,
a the length and the
width. When the rectangle is rotated around the width 3 a.
rotation axis in the following two ways, the ratio of
the volumes of cylinders is 2:1. Find the ratio of the
volumes of cylinders when a rectangle has a length
that is three times as long as the width is revolved
around the rotation axis in the following two ways.

5 cm 5 cm

10 cm 10 cm

A B

81Geometry