13/5 is the answr,that`s wat i`m getting.someone plz clarify.
I`l then explain my method properly if i can........though i`m nt good at it
Three vertices are chosen at randomly from seven vertices of regular seven sided polygon. Probability that they form vertices of an isosceles triangle is:
a) 1/7
b) 1/3
c) 3/7
d) 3/5
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2 Answers
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262yes even i am getting 3/5
now look at the picture,
1,2,7 form an isoceles triangle *(7 times)
1,3,6 form an isoceles triangle *(7 times)
1,4,5 form an isoceles triangle *(7 times)
hence total 21 such triangles can be formed.
total no. of triangles = 7C3 = 35
hence propbability = 21/ 35 = 3/5 (Ans.)