A student walks from his house at 21/2 km/h and reaches

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A student walks from his house at 2¹/₂ km/h and reaches his school late by 6 min. Next day, he increase his speed by 1 km/h and reaches 6 min before school time. How far is the school form his house?

1. 5/4 km
2. 7/4 km
3. 9/4 km
4. 11/4 km

Correct Option: B

Let the required distance = L
According to the question,
L/(5/2) - L/(7/2) = 12/60 (difference between two times = 6 + 6 =12 min)
⇒ 2L/5 - 2L/7 = 1/5
⇒ 14L - 10L = 7
⇒ 4L = 7
⇒ L = 7/4 km