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WAEC 2019 · Paper 1 · Q21

The total surface area of a solid cylinder is 165 cm2165\text{ cm}^2. If the base diameter is 7 cm7\text{ cm}, calculate its height. [Take π=227]\left[\text{Take }\pi = \frac{22}{7}\right]

Worked solution (try it first)
  1. Radius =7÷2=3.5= 7 \div 2 = 3.5 cm.
  2. Total surface area: 2πr(r+h)2\pi r(r + h), and 2πr=2×227×3.52\pi r = 2 \times \frac{22}{7} \times 3.5
    =22= 22.
  3. So 22(3.5+h)=16522(3.5 + h) = 165.
  4. Divide by 22: 3.5+h=7.53.5 + h = 7.5.
  5. So h=4.0h = 4.0 cm, option C.

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