Question

There are two beautiful lakes near a village. People come for boating and picnics in both the lakes. The village Panchayat is worried that with the noise of the boats the birds will stop coming. The Panchayat wants motor boats in only one lake. The other lake will be saved for the birds to make their nests.



(a) How many cm is the length of the boundary of lake A in the drawing? __________ (use thread to find out)
(b) What is the length of the boundary of lake B in the drawing?
(c) How many kilometres long is the actual boundary of lake A?
(d) How many kilometres long is the actual boundary of lake B?
(e) A longer boundary around the lake will help more birds to lay their eggs. So which lake should be kept for birds? Which lake should be used for boats?
(f) Find the area of lake B on the drawing in square cm. What is its actual area in square km?

Answer 1

(a) When we measure the boundary of lake A with the help of thread, it comes out to be
around 30 cm.

(b) When we measure the boundary of lake B with the help of thread, it comes out to be
around 25 cm.

(c) Here, the scale is 1 cm = 1 km
So, length of the actual boundary of lake A = 30 km

(d) Here, the scale is 1 cm = 1 km
So, length of the actual boundary of lake B = 25 km

(e) The boundary around the lake A is more than the boundary around the lake B. So, lake A should be kept for birds and lake B should be used for boats.

(f) Lake B has 15 fully filled squares and 11 half -filled or more than half - filled squares.
Area of 15 fully filled squares = 15 $\times$ 15
= 225 square cm

We consider the area of every single half - filled or more than half - filled square as 1 centi metre square.

Thus, the area of 11 such squares = 11 $\times$ 11
= 121 square cm

So, total area of lake B = 225 + 121
= 346 square cm

We are given 1 cm on drawing = 1 km on ground
Therefore, 346 square cm on drawing = 346 km