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A student measured the length of a room and obtained the ...

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

Correct answer is D

Let the actual length of the room = y m

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

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

y = 4.2 m