Base of a right prism is a rectangle, the ratio of whose length and breadth is 3 : 2. If the height of the prism is 12 cm and total surface area is 288 sq.cm the volume of the prism is :
Options:
A .  291 cm3
B .  288 cm3
C .  290 cm3
D .  286 cm3
Answer: Option B Let the length of base be 3a cm and breadth be 2a cm Total surface area of prism : = [Perimeter of base × height] + [2 × Area of base] = [2 (3a + 2a) × 12 + 2 × 3a × 2a] sq.cm = (120a + 12a2) sq.cm According to the question, 120a + 12a2 = 288 ⇒ a2 + 10a = 24 ⇒ a2 + 10a - 24 = 0 ⇒ a2 + 12a - 2a - 24 = 0 ⇒ a (a + 12) - 2 (a + 12) = 0 ⇒ (a - 2)(a + 12) = 0 ⇒ a = 2 because a $$ \ne $$ -12 ∴ Volume of prism : = Area of base × Height = (3a × 2a × 12)cu.cm = 72a2 cu.cm = (72 × 2 × 2)cu.cm = 288 cu.cm
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