NCERT Solutions Ganita Prakash (Part 1) Chapter 3 The Mechanism of Counting — Figure it Out

Book page 54 Updated on2026-09-05

Q1.
Suppose you are using the number system that uses sticks to represent numbers, as in Method 1. Without using either the number names or the numerals of the Hindu number system, give a method for adding, subtracting, multiplying and dividing two numbers or two collections of sticks.
Answer

Every one of the four operations can be done by moving sticks about. Call the two collections A and B.

OperationWhat to do with the sticksWhat the answer is
A + BPush the two heaps together into one heap.The combined heap
A − BPair each stick of B with a stick of A and take both away. Stop when B is exhausted.The sticks of A still unpaired
A × BFor every single stick of B, lay out one fresh copy of the whole heap A. Then pool all those copies together.The pooled heap
A ÷ BFrom A, keep pulling out bunches, each bunch matched one-to-one with B. Beside each completed bunch place one marker stick.The markers are the quotient; the sticks left in A that cannot fill a bunch are the remainder
Why it happens: each rule is the meaning of the operation, stripped of names. Addition is putting collections together; subtraction is removing a matched part; multiplication is repeated addition of equal collections; division is repeated subtraction of equal collections, and the quotient is how many times you could do it — which is itself a number, so it too gets its own collection of markers. Nothing here needs the word “seven”.
Check it yourself: take A = 7 sticks and B = 3 sticks. Pull out bunches of 3: you get two bunches (two markers) and 1 stick left over. That is 7 ÷ 3 = 2 remainder 1 — obtained without saying a single number.
Q2.
One way of extending the number system in Method 2 is by using strings with more than one letter — for example, we could use ‘aa’ for 27. How can you extend this system to represent all the numbers? There are many ways of doing it!
Answer

Use all the strings of a given length before moving to the next length, in dictionary order.

Length of stringStringsNumbers coveredHow many
1 lettera, b, c, …, z1 – 2626
2 lettersaa, ab, ac, …, az, ba, …, zz27 – 702262 = 676
3 lettersaaa, aab, …, zzz703 – 18278263 = 17576
4 lettersaaaa, …, zzzz18279 – 475254264 = 456976
26 + 676 = 702
702 + 17576 = 18278
18278 + 456976 = 475254

The first two-letter string is aa, and it lands on 27 — exactly as the book suggests.

Why it happens: there are 26k strings of length k, and the total 26 + 262 + 263 + … grows without limit. So every number gets a string, and no string is wasted — each number has exactly one name and each name belongs to exactly one number. That makes this an unending standard sequence, which the plain 26-letter version was not.
Try This: a simpler extension is a, b, …, z, then aa, bb, …, zz, then aaa, bbb, …, zzz. It also never runs out, but it uses only 26 new names at each stage instead of 26k, so numerals grow very long. Both are correct — the first is far more efficient.
Q3.
Try making your own number system.
Answer

Here is one worked example; yours may look completely different, and that is fine. Choose three symbols and let each stand for a group ten times the one before.

● = 1    ■ = 10    ★ = 100
NumberGrouped asMy numeral
71+1+1+1+1+1+1●●●●●●●
2310 + 10 + 1 + 1 + 1■■●●●
140100 + 10 + 10 + 10 + 10★■■■■
306100 + 100 + 100 + 1+1+1+1+1+1★★★●●●●●●

Before you settle on a system, test it against the three demands the chapter has already made:

  • Is it unending? Mine is not yet — it stops just short of 1000. I must either add a symbol for 1000 or switch to positions.
  • Is it easy to count with? Yes — the symbols have a fixed order.
  • Is it easy to compute with? Yes, because each landmark is 10 times the last, so ten ● become one ■ and ten ■ become one ★.
Why it happens: choosing landmark numbers that are all powers of one number is what makes regrouping mechanical. If you had chosen ● = 1, ■ = 7, ★ = 30, the system would still work for writing numbers, but you would have to remember two different exchange rates instead of one.
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