dear tejas,

the answer is 9km.

if you solve it traditionally you will land up in an

equation of fourth degree which is highly time

consuming to solve. here is the trick to solve

quickly.

from the question it is clear that there is a right

angled triangle with sides 9 and 3+2r containing the

right angle.

hence value of 3+ 2r can be 12 or 40 .

if try with these two values you will find that 12 is

the correct value of 3+2r.

hence r = 4.5 km or d = 9 km.

bhakta

--- Tejas Mehta <

devdas83@...> wrote:

> Hi group,

> this one is straight from CAT 2001,plz help me to

> solve it.

>

> A certain city has a circular wall around it,and

> this

> wall has four gates pointing north,south,east and

> west. A house stands outside the city, three kms

> north

> of the north gate, and it can just be seen from a

> point nine kms east of the south gate. What is the

> diameter of the wall that surrounds the city?

>

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