Let the length of the room is represented by 'l' and breadth by 'b'.

Given that length and breadth of the room is increased by 1m.

= > (l + 1) * (b + 1).

We know that Area of floor = l * b.

Given that area of the floor is increased by 21 m^2.

= > (l + 1) * (b + 1) = lb + 21

= > (l + 1) * (b + 1) - lb = 21

= > lb + l + b + 1 - lb = 21

= > l + b + 1 = 21

= > l + b = 20 -------- (1)

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Given that length is increased by 1m and breadth is decreased by 1m.

= > length = l + 1

= > breadth = b + 1.

Given that area is decreased by 5m.

= > (l + 1) * (b - 1) = lb - 5

= > (l + 1) * (b - 1) - lb = -5

= > lb - l + b - 1 - lb = -5

= > -(l - b) = -4

= > l - b = 4 ------- (2)

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On solving (1) & (2), we get

= > l + b = 20

= > l - b = 4

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2b = 24

b = 12.

Substitute b = 12 in (1), we get

= > l + b = 20

= > l + 12 = 20

= > l = 8.

Now,

We know that perimeter of the floor = 2(l + b)

= > 2(8 + 12)

= > 2(20)

= > 40m.

error in question replace 3 by 5