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### Question

A gun is fired towards a circular board consisting of two concentric circles of radii 10 and 4 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**

${21/25}$.

**B**

${7/10}$.

**C**

1/2.

**D**

${21/40}$.

**Soln.**

**Ans: a**

The area of the ring is equal to the difference of the areas of the two circles. π($10^2 - 4^2$) = 84π sq. cm. The total area is π × 10^{2} = 100π. The probability of hitting the ring is ${84π}/{100π}$ = ${21/25}$.