NCERT Solutions for Class 4th Maths Chapter 1 Radius, diameter and a design made with a compass — Let Us Do
Book page 18 Updated on2026-09-19
Q1.
Fold the circular paper in half. Fold this half again in half. The length of the diameter is ___________ (half/double) of the length of radius.
A circle with one diameter and one radius drawn.
Answer
The length of the diameter is double the length of the radius.
Fold the round paper in half. The crease you get is a diameter.
Fold that half in half again. The new crease reaches only from the centre to the
border — that is a radius.
Lay the radius along the diameter. It covers exactly half of it. Do it twice and the
whole diameter is covered.
Why it happens: The second fold folds the half circle about its
centre, so it cuts the first crease into two equal pieces. Each piece is a radius, and
two of them make the diameter.
Q2.
A circle can be made easily using a compass. Ask your teacher to help you use a compass. Make the following design.
The design made with a compass: a circle with six more circles of the same radius drawn round it.
Answer
Keep the compass open at the same width all the
way through. That is the secret of the design.
Step 1 — Open the compass a little, say 3 cm. Put the needle on a
point and draw one full circle.
Step 2 — Without changing the compass width, put the needle anywhere on
that circle and draw another circle.
Now put the needle where the new circle cuts the first one, and draw again.
Go on round the first circle in the same way. After six circles you come back to
where you started.
Step 3 — Colour the petal shapes that have been formed.
Why it happens: Because the compass stays open at the same
width, every circle has the same radius. Six such circles fit exactly round one circle,
and the parts where they overlap make the six petals.
Q3.
Look at the carpet design. A beautiful circle, right? Mark the centre, radius, and the diameter of the circular design with any colour of your choice.
A circle with one diameter and one radius drawn.
Answer
The carpet has a big round design with six petals meeting at the middle.
Centre — the point in the middle where all six petals meet. Mark it
with a dot and write C.
Radius — draw a line from that dot straight out to the edge of the round
design, along one petal. Colour it green.
Diameter — draw a line right across the design, from one edge through the
centre to the opposite edge. Colour it red.
Check with a scale: the red line should measure exactly twice the green line.
Why it happens: The six petals are drawn with the same compass
width, so they all meet at one point — and that point is the centre of the whole
design.