Question : The total surface area of a square-based right pyramid is 1536 m2, of which 37.5% is the area of the base of the pyramid. What is the volume (in m3) of this pyramid?
Option 1: 3048
Option 2: 3072
Option 3: 3144
Option 4: 3108
Correct Answer: 3072
Solution : Given: Total surface area of pyramid = 1536 m 2 Area of base = 37.5% of total surface area = $\frac{37.5}{100}\times1536$ = $\frac{3}{8}\times1536$ = $576$ Remaining area = 1536 – 576 = 960 $\therefore$ lateral surface area = 960 m 2 Area of square base = 576 ⇒ $\text{side}^2=576$ $\therefore \text{side}=24$ Perimeter of base = 4 × 24 = 96 We know that, Lateral surface area of pyramid = $\frac{1}{2}$ × perimeter of base × slant height ⇒ $960 = \frac{1}{2} \times 96\times$ slant height $\therefore$ Slant height = 20 $\text{Height} = \sqrt{\text{slant height}^2-(\frac{\text{side}}{2})^2}$ = $\sqrt{20^2-12^2}$ = $16$ Now, Volume of pyramid = $\frac{1}{3}$ × area of base × height = $\frac{1}{3}\times576\times16$ = $3072$ m 3 Hence, the correct answer is 3072.
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