A student measured the length of a room and obtained the measurement of 3.99m. If the percentage error of is measurement was 5% and his own measurement was smaller than the length , what is the length of the room?

  • A 3.78m
  • B 3.80m
  • C 4.18m
  • D 4.20m
  • E 4.788m
waec 1998mathematics

The correct answer is D. 4.20m

Let the actual length of the room = y m

\(\therefore \frac{y - 3.99}{y} \times 100% = 5%\)

\(100(y - 3.99) = 5y \implies 100y - 399 = 5y\)

\(100y - 5y = 399 \implies y = \frac{399}{95}\)

y = 4.2 m

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