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In a room, there are \(n\) persons whose average height is \(160 \ \text{cm}\). If \(m\) more persons, whose average height is \(172 \ \text{cm}\), enter the room, then the average height of all…

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In a room, there are nn persons whose average height is 160 cm160 \ \text{cm}. If mm more persons, whose average height is 172 cm172 \ \text{cm}, enter the room, then the average height of all persons in the room becomes 164 cm164 \ \text{cm}. Then m:nm: n is
  1. 1:21 : 2
  2. 1:31 : 3
  3. 3:13 : 1
  4. 2:12 : 1

Answer and explanation

Correct answer: A - \(1 : 2\)

The total heights must balance: 160n + 172m = 164(n + m). This simplifies to 8m = 4n, so m : n = 1 : 2. The reversed ratio 2 : 1 mixes up which group is larger; the new average sits nearer 160, so the original group must be bigger.

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  • IPMAT Indore

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