Chapter 6
Measuring Space: Perimeter and Area
CBSE Class 9
Mathematics Solutions
Educart Mathematics class Class 9 NCERT Exemplar cover
Question:

The ratio of the perimeters of two circles is 5 : 4. What is the ratio of their radii?                                  [Page No. 130]

Answer: Verified

Perimeter (circumference) of circle = 2πr2\pi r

Let radii be r1r_1 and r2r_2.

C1C2=2πr12πr2=r1r2\frac{C_1}{C_2} = \frac{2\pi r_1}{2\pi r_2} = \frac{r_1}{r_2}

Given: C1C2=54\frac{C_1}{C_2} = \frac{5}{4}

Therefore, r1:r2=5:4r_1 : r_2 = 5 : 4

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(All Q's of this Chapter solved)
More NCERT Questions
Find the area of a quadrant of a circle whose circumference is 66 cm. Show how we can use two identical copies of a trapezium to make a parallelogram. How will this give us the formula for the area of a trapezium? Two rectangles have the same area and the same perimeter. Does this mean that they are congruent to each other? By dividing a trapezium into two triangles show that its area is, half the sum of the parallel sides multiplied by the height (the same formula as the one given above).