NCERT Solutions for Class 5th Maths Chapter 11 Preetha's desk: how many of each tile would cover it — Let Us Do
Book page 144 Updated on2026-09-19
Q1.
Look at the different tiles on her desk and answer how many of the following shapes will cover the desk. (a) Green triangles __________
Preetha's desk with the tiles she has put on it — one blue square, one red triangle and one green triangle.
Answer
108 green triangles.
The blue tile is one square. The green tile is half a square. The red tile covers four and a half squares.
Count the squares of the desk. 9 across and 6 down, so 9 × 6 = 54 squares.
Look at the green tile. It sits inside one square and covers exactly half of it.
See how many greens fill one square. Two halves make one whole, so 2 green triangles fill 1 square.
Multiply. 54 squares × 2 = 108.
Squares on the desk = 9 × 6 = 54 Green triangles in 1 square = 2 Green triangles for the whole desk = 54 × 2 = 108 green triangles
Why it happens: The green tile is smaller than the square, so it takes more of them. Exactly twice as many, because it is exactly half the size.
Q2.
Look at the different tiles on her desk and answer how many of the following shapes will cover the desk. (b) Red triangles __________
Preetha's desk with the tiles she has put on it — one blue square, one red triangle and one green triangle.
Answer
12 red triangles.
Measure the red tile on the grid. Its straight top edge is 3 squares long and its straight side edge is 3 squares long.
Think of the square it came from. A 3-by-3 square holds 3 × 3 = 9 small squares. The red triangle is exactly half of that square.
Find its area. Half of 9 is 4 and a half. So one red triangle covers 4½ squares.
Share the desk out. 54 ÷ 4½ = 12.
Red triangle = half of a 3 × 3 square Area of red triangle = (3 × 3) ÷ 2 = 9 ÷ 2 = 4½ squares Red triangles needed = 54 ÷ 4½ Two red triangles = 9 squares, so 54 ÷ 9 = 6 pairs Red triangles = 6 × 2 = 12 red triangles
An easier way to do the division: Halves are awkward to divide by. So join two red triangles together — they make a 3 × 3 square of 9 small squares. The desk holds 54 ÷ 9 = 6 such big squares, and each one needs 2 red triangles. 6 × 2 = 12.
Check it yourself: 12 red triangles × 4½ squares each = 12 × 4 + 12 × ½ = 48 + 6 = 54 squares. That is the whole desk. ✓
Q3.
Look at the different tiles on her desk and answer how many of the following shapes will cover the desk. (c) Blue squares __________
Preetha's desk with the tiles she has put on it — one blue square, one red triangle and one green triangle.
Answer
54 blue squares.
Look at the blue tile. It fits exactly on one square of the grid.
Count the squares of the desk. 9 across, 6 down.
Multiply. 9 × 6 = 54.
Blue squares = 9 × 6 = 54 blue squares
Now compare all three tiles.
Tile
How much it covers
Number needed
Green triangle
½ square
108
Blue square
1 square
54
Red triangle
4½ squares
12
Why the pattern goes that way: The desk never changes. Only the tile changes. A bigger tile fits fewer times; a smaller tile fits more times. The green tile is half the blue one, so twice as many are needed. The red tile is 4½ times the blue one, so only about a ninth as many are needed.