Find the diameter of a sphere whose surface area is 154 cm².

Surface area of sphere = 4πr².

Given, surface area = 154 cm².

∴ 4πr² = 154

$4 \times \dfrac{22}{7} \times r^2 = 154 \\[1em] \Rightarrow r^2 = \dfrac{154 \times 7}{88} \\[1em] \Rightarrow r^2 = \dfrac{1078}{88} \\[1em] \Rightarrow r^2 = 12.25 \\[1em] \Rightarrow r = \sqrt{12.25} \\[1em] \Rightarrow r = 3.5 \text{ cm}.$

Diameter = 2 × radius = 2 × 3.5 = 7 cm.

Hence, the diameter of sphere = 7 cm.