Question

If the difference between the circumference and diameter of a circle is $30cm$, then the radius of the circle must be:

• A. $6cm$
• B. $7cm$
• C. $5cm$
• D. $8cm$

Answer 1

The correct option is B $7cm$

As we know that,

Circumference of circle $=2\pi r$

Diameter of circle $=2r$

Now, accordig to the question-

$2\pi r-2r=30cm$

$2r(\frac{22}{7}-1)=30$

$\Rightarrow r=\frac{15\times 7}{15}$

$\Rightarrow r=7cm$