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### Question

A gun is fired towards a circular board consisting of two concentric circles of radii 18 and 15 cm. If each bullet is able to hit the board, what is the probability that it will strike the ring, i.e., the area between the inner and outer circles?

**A**

${11/36}$.

**B**

${11/41}$.

**C**

1/2.

**D**

${11/51}$.

**Soln.**

**Ans: a**

The area of the ring is equal to the difference of the areas of the two circles. π($18^2 - 15^2$) = 99π sq. cm. The total area is π × 18^{2} = 324π. The probability of hitting the ring is ${99π}/{324π}$ = ${11/36}$.