#### Question

In each example given below, radius of base of a cylinder and its height are given. Then find the curved surface area and total surface area.

(1) r = 7 cm, h = 10 cm

(2) r = 1.4 cm, h = 2.1 cm

(3) r = 2.5 cm, h = 7 cm

(4) r = 70 cm, h = 1.4 cm

(5) r = 4.2 cm, h = 14 cm

#### Solution

We know that

Curved surface area of a cylinder = 2 π rh

Total surface area = 2 πr (h + r)

(1) r = 7 cm, h = 10 cm

Curved surface area of a cylinder = 2 π rh = 2 π × 7 × 10 = 140 π = 140 × `22/7` = 440 sq cm

Total surface area = 2 π r (h + r) = 2 × `22/7` (10 + 7) = 748 sq cm

(2) r = 1.4 cm, h = 2.1 cm

Curved surface area of a cylinder = 2 π rh = 2 × `22/7` × 1.4 × 2.1 = 18.48 sq cm

Total surface area = 2 π r (h + r) = 2 × `22/7` ×1.4 (2.1 + 1.4) = 30.8 sq cm

(3) r = 2.5 cm, h = 7 cm

Curved surface area of a cylinder = 2 π rh = 2 × `22/7` × 2.5× 7 = 110 sq cm

Total surface area = 2 π r (h + r) = 2 × `22/7` × 2.5 (2.5 + 7) = 149.28 sq cm

(4) r = 70 cm, h = 1.4 cm

Curved surface area of a cylinder = 2 π rh = 2 × `22/7` × 70 × 1.4 = 616 sq cm

Total surface area = 2 π r (h + r) = 2 × `22/7` × 70 (70 + 1.4) = 31416 sq cm

(5) r = 4.2 cm, h = 14 cm

Curved surface area of a cylinder = 2 π rh = 2 × `22/7` × 4.2 × 14 = 369.6 sq cm

Total surface area = 2 π r (h + r) = 2 × `22/7` × 4.2 (4.2 + 1.4) = 480.48 sq cm