NCERT Solutions for Class 5th Maths Chapter 11 Perimeter of shapes with equal sides; drawing rectangles to a given perimeter — Let Us Do
Book page 142 Updated on2026-09-19
Q1.
Find the perimeter of the following shapes. All sides of the following shapes are equal. (First shape.)
A shape with five equal sides. One side is marked.
Answer
Perimeter = 20 cm.
Five equal sides. Walk round: 4 + 4 + 4 + 4 + 4 = 20 cm.
Count the sides. The shape has 5 sides.
Read one side. One side is 4 cm, and the question says all sides are equal. So every side is 4 cm.
Add all the sides. 4 + 4 + 4 + 4 + 4 = 20.
Write the unit. The answer is a length, so it is in cm.
Why it happens: Perimeter is the whole walk round the outside. Walking round this shape means walking along 5 sides, one after another. Each walk is 4 cm long, so five walks are 5 × 4 = 20 cm.
Short cut: When all the sides of a shape are equal, you do not have to add. Just multiply: number of sides × length of one side.
Q2.
Find the perimeter of the following shapes. All sides of the following shapes are equal. (Second shape.)
Two triangles joined at one point. All the sides are equal.
Answer
Perimeter = 30 cm.
Two triangles joined at one point. The outside has 6 equal sides.
Trace the outside with your finger. Start at the top-left corner. Go along the top (1 side), slide down to the middle point (2), down to the bottom-left corner (3), along the bottom (4), up to the middle point (5), and back up to the top-left corner (6).
Count what you walked. That is 6 sides.
Use the length given. All sides are equal and one is 5 cm, so each of the 6 sides is 5 cm.
Multiply. 6 × 5 = 30.
Number of sides on the outside = 6 Perimeter = 6 × 5 cm Perimeter = 30 cm
Why it happens: The shape is made of two triangles that touch at one point. Each triangle gives 3 sides to the outside — its top (or bottom) and its two slanting sides. 3 + 3 = 6 sides in all. The point where they touch is not a side, so nothing is added there.
Careful: Do not count 8 sides. The two lines that cross in the middle are not four separate straight edges of the outside — each one is split at the touching point into two of the six sides you already counted.
Q3.
Draw two rectangles each having the following perimeter: (a) 26 cm
Answer
Two rectangles with perimeter 26 cm: one of 8 cm × 5 cm, and one of 10 cm × 3 cm.
Remember what perimeter means for a rectangle. A rectangle has 2 long sides and 2 short sides. So perimeter = length + length + breadth + breadth.
Halve the perimeter. One long side and one short side together make half the perimeter. 26 ÷ 2 = 13 cm.
Split 13 into two whole numbers. 8 + 5 = 13, and 10 + 3 = 13.
Draw them. Draw one rectangle 8 cm long and 5 cm broad. Draw another 10 cm long and 3 cm broad.
Two different rectangles, both with a 26 cm border.
Check the first: 8 + 5 + 8 + 5 = 26 cm ✓ Check the second: 10 + 3 + 10 + 3 = 26 cm ✓
Why halving works: Going round a rectangle you walk the length twice and the breadth twice. So the whole trip is two lots of (length + breadth). Half the trip is exactly one length plus one breadth.
Other correct answers: 9 cm × 4 cm, 7 cm × 6 cm, 11 cm × 2 cm, 12 cm × 1 cm — any pair that adds to 13 cm.
Q4.
Draw two rectangles each having the following perimeter: (b) 18 cm
Answer
Two rectangles with perimeter 18 cm: one of 6 cm × 3 cm, and one of 7 cm × 2 cm.
Halve the perimeter. 18 ÷ 2 = 9 cm. This is one length plus one breadth.
Split 9 into two whole numbers. 6 + 3 = 9, and 7 + 2 = 9.
Draw them. One rectangle 6 cm by 3 cm, and one 7 cm by 2 cm.
Both rectangles need exactly 18 cm of ribbon to go round.
Check the first: 6 + 3 + 6 + 3 = 18 cm ✓ Check the second: 7 + 2 + 7 + 2 = 18 cm ✓
Did you notice? The 6 cm × 3 cm rectangle covers 18 square cm, but the 7 cm × 2 cm one covers only 14 square cm. Same border, different amount of cloth. You will meet this idea again on page 148.
Other correct answers: 5 cm × 4 cm and 8 cm × 1 cm — any pair that adds to 9 cm.