NCERT Solutions for Class 9th Maths Chapter 1 After Exercise Set 1.1 — Think and Reflect

Book page 5 Updated on2026-09-08

Q1.

What are the standard widths for a room door? Look around your home and in school.

Answer

Common widths used in Indian homes and schools:

Door	Usual width	In feet
Main entrance door	900–1000 mm	3 – 3.3 ft
Bedroom / room door	750–900 mm	2.5 – 3 ft
Bathroom / toilet door	700–750 mm	2.3 – 2.5 ft
Classroom door	900–1200 mm	3 – 4 ft

Doors are usually 2.0–2.1 m (about 6.5–7 ft) tall.

Try This: Measure five doors around you and record each as an ordered pair (width, height) in centimetres. Then treat width as x and height as y and plot the five points. You will see the points cluster in a narrow band — doors are not made in random sizes, and the plot shows that at a glance.

Why it happens: Measure the clear opening, not the frame: when a door is fully open the leaf and hinges still stand in the way, so the usable gap is typically 25–50 mm less than the frame width.

Q2.

Are the doors in your school suitable for people in wheelchairs?

Answer

Test each door against three things, not just one:

Clear width. India’s Harmonised Guidelines for Barrier Free Built Environment ask for a clear opening of at least 900 mm. A 750 mm bathroom door fails this.
Threshold. A raised sill or step at the door stops a wheelchair even if the door is wide. The floor should be level, or ramped at a gentle slope of about 1 : 12.
Turning space. A wheelchair needs roughly a 1500 mm × 1500 mm clear circle to turn, so a wide door opening into a narrow corridor is still not usable.

In most school buildings the classroom doors pass the width test and the toilet doors fail it — which is exactly the door that matters most.

Try This: Make a table of every door in your school block with columns: width, threshold height, and pass/fail. That table is a small accessibility audit, and it is the sort of evidence a school can actually act on.

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