Q23 of 180 Page 1

If a 1.5 m tall girl stands at a distance of 3 m from a lamp-post casts a shadow of length 4.5 m on the ground then find the height of the lamp-post.

The diagram is shown below.


Height of the girl, KL = 1.5m


Distance of girl from lamp post, LI = 3 m


Shadow of the girl, JL = 4.5 m


Height of the lamp post, HI, to be calculated.


⇒ JI = JL + LI = 4.5 + 3 = 7.5 m




From the above figure, ∠HJI = ∠KJL


⇒


⇒


⇒


∴ HI = 2.5 m


Hence, the height of the lamp post is 2.5 m.


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