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Imagine circle B tocuhes the biggest circle at D and circle A touched the biggest circle at D.

Now from the question OC = 9, OB = 6

Therefore, BC (Radius of circle B) = OC - OB = 3

Now ratio AD / BC = 2 / 3

Hence AD (Radius of circle A) = 2

Finally AB = AD + BC = 2+3= 5

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Solution



Given:
    • A and B are centers of two circles touching each other
      o The ratio of radius of two circles= 2 : 3 respectively.
    • The radius of circle with centre O = 9
      o OB = 6

To find:
    • AB =?

Approach and Working

AB = Radius of circle with centre A + Radius of circle with centre B
    • So, we need to know the radius of both the smaller circles.

We are given OB = 6
    • OB = Radius of circle with centre O - Radius of circle with centre B
    • = 9 - Radius of circle with centre B = 6
    • Radius of circle with centre B =3
Hence, Radius of circle with centre A = 2
Thus, AB =5

Hence, the correct answer is C.
Correct answer: Option C
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