Given: If the manwalks@3 km/hr, he reaches 40 min early If the manwalks@2 km/hr, he reaches 40 min late Formula Used: Total distacne = Speed × Time Caluclation: Let the distance between residence and office be D The usual speed is S
km
hr
and usual time be T hr Now, According to the question D=3(T−40∕60)⋯−(ii) And D=2(T+40∕60)⋯ (iii) From (ii) and (iii), we get 3(T−40∕60)=2(T+40∕60) ⇒3T−2=2T+4∕3 ⇒T=(2+4∕3)hr ⇒T=10∕3hr From (ii) D=3[(10∕3)−(40∕60)]km ⇒D=3[(10∕3)−(2∕3)]km ⇒D=3(8∕3)km ⇒D=8km ∴ The distance between residence and office is 8km.