NCERT Solutions for Class 5th Maths Chapter 2 Building a whole out of chosen kit pieces — Let Us Do (Question 3)

Book page 20 Updated on2026-09-19

Q1.
Do as instructed using your fraction kit: Make a whole using only 1/6 and 1/12 pieces.
Answer

One good answer: five 1/6 pieces and two 1/12 pieces.

5 × 1/6 = 5/6
2 × 1/12 = 2/12 = 1/6
5/6 + 1/6 = 6/6 = 1 whole
1/61/61/61/61/6 1/121/12 Five 1/6 pieces + two 1/12 pieces = one whole 5/6 + 2/12 = 10/12 + 2/12 = 12/12 = 1
The last one-sixth space is filled by two one-twelfth pieces.

Other correct answers (each row makes exactly one whole):

Pieces of 1/6Pieces of 1/12Check
5210/12 + 2/12 = 1
448/12 + 4/12 = 1
366/12 + 6/12 = 1
284/12 + 8/12 = 1
1102/12 + 10/12 = 1
Why it happens: One 1/6 piece is the same size as two 1/12 pieces. So every time you remove a 1/6 piece you can put two 1/12 pieces in its place, and the whole is still full.
Q2.
Make a whole using 1/12, 1/4, and 1/2 pieces.
Answer

One 1/2 piece + one 1/4 piece + three 1/12 pieces = one whole.

Change every piece into twelfths first, because 12 works for 2, 4 and 12.

  1. 1/2 = 6/12 (since 12 ÷ 2 = 6)
  2. 1/4 = 3/12 (since 12 ÷ 4 = 3)
  3. That is 6/12 + 3/12 = 9/12 so far.
  4. 12/12 − 9/12 = 3/12, so add three 1/12 pieces.
1/2 + 1/4 + 1/12 + 1/12 + 1/12
= 6/12 + 3/12 + 3/12
= 12/12 = 1 whole
1/21/41/121/121/12 6/12 + 3/12 + 3/12 = 12/12 = 1
Three different sizes of piece, one full strip.
Another correct answer: two 1/4 pieces + one 1/4 piece + three 1/12 pieces will not do, because it has no 1/2. But 1/2 + two 1/12 + ... always check the total comes to exactly 12/12.
Q3.
Make a whole using any five pieces of the same size.
Answer

Use five 1/5 pieces.

1/5 + 1/5 + 1/5 + 1/5 + 1/5 = 5/5 = 1 whole
1/51/51/51/51/5 Five equal pieces, so each piece must be 1/5 5/5 = 1
If five equal pieces make one whole, each piece is one-fifth.
Why it happens: If all five pieces are the same size and they exactly fill the whole, then the whole has been cut into 5 equal parts. That is what 1/5 means. No other same-size piece will work — five 1/4 pieces would be too much (5/4) and five 1/6 pieces too little (5/6).
Q4.
Make a whole using any seven pieces.
Answer

One good answer: five 1/6 pieces and two 1/12 pieces — that is 7 pieces in all.

5/6 + 2/12
= 10/12 + 2/12
= 12/12 = 1 whole   (pieces used: 5 + 2 = 7)

Another answer: one 1/2 piece and six 1/12 pieces — also 7 pieces.

1/2 + 6/12 = 6/12 + 6/12 = 12/12 = 1 whole   (pieces used: 1 + 6 = 7)
1/2 six 1/12 pieces 1 + 6 = 7 pieces, and they fill the strip exactly
Seven pieces of two different sizes, filling one whole.
How to invent your own: Turn every piece into twelfths. Then just make seven numbers of twelfths add up to 12 — for example 6 + 2 + 1 + 1 + 1 + 1 = 12 gives 1/2 + 1/6 + four 1/12 pieces, which is also 7 pieces.
Q5.
Play in a group with this kit and find other interesting combinations to make a whole. Write or draw your findings.
Answer

Work in a group. One child lays pieces on the whole strip, another writes down the fractions, and the group checks that the total is exactly 1.

Sample answer — findings written by a group:

Combination we madeNumber of piecesCheck in twelfths
1/2 + 1/3 + 1/636/12 + 4/12 + 2/12 = 12/12
1/2 + 1/4 + 1/436/12 + 3/12 + 3/12 = 12/12
1/3 + 1/3 + 1/6 + 1/644/12 + 4/12 + 2/12 + 2/12 = 12/12
1/4 + 1/4 + 1/4 + 1/6 + 1/1253/12 + 3/12 + 3/12 + 2/12 + 1/12 = 12/12
1/2 + 1/6 + 1/6 + 1/12 + 1/1256/12 + 2/12 + 2/12 + 1/12 + 1/12 = 12/12
Twelve 1/12 pieces1212/12

Two things our group noticed:

  1. Every combination adds up to 12 twelfths. Twelfths work well because 2, 3, 4, 6 and 12 all divide 12.
  2. The more pieces you use, the smaller the pieces have to be.
Try this at home: Make a whole using pieces that are all different sizes. 1/2 + 1/3 + 1/12 + 1/12 works: 6/12 + 4/12 + 1/12 + 1/12 = 12/12.
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