Question

FIND THE AREA OF THE CIRCULAR RING FORMED BY THE CIRCUMFERENCE OF TWO CONCENTRIC CIRCLE OF RADII 11M AND 4M.ALSO FIND THE COST OF PAINTING THIS RING AT THE RATE OF RS 21 PER M²

Answer 1

Area of ring = area of larger circle - area of smaller circle.

So,
Area of larger circle (r = 11m) =
$\pi {r}^{2} = \frac{22}{7} \times 121$
Area of smaller circle (r=4m) =
$\pi {r}^{2} = \frac{22}{7} \times 16$
So,
Area of ring =
$\frac{22}{7} \times 121 - \frac{22}{7} \times 16 = \frac{22}{7} (121 - 16)$
$= \frac{22}{7} \times 105 \\ = 22 \times 15 \\ = 330 {m}^{2}$

Cost of painting =
$21 \times 330 = 6930$

Hope this will be helping you

WARM REGARDS
Sahil khirwal

Answer 2

Hi.
Area of the circle of radius 11m = π × r1 ×r1 
                                              A1  = 22/7 × 11 v 11
                                              A1  = 2662/7

Area of the circle of radius 4m = π × r2 × r2
                                              A2   =  22/7 × 4 × 4
                                              A2  = 352/7
Area of the ring = A1 - A2
                         = (2662 - 352) / 7
                         = 330 m²
Also, The cost of painting the ring at 21 per m² = 21 × Area of the ring
                                                                          = 21 × 330
                                                                          = Rs. 6930  
Hope it will help u.
If u have any query, u can ask me.
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