NCERT Solutions Ganita Prakash Chapter 1 Figure it Out — Patterns in Numbers

Book page 3 Updated on2026-09-05

Q1.
Can you recognise the pattern in each of the sequences in Table 1?
Answer

Yes. Each sequence in Table 1 is built by one simple rule, repeated again and again:

  • All 1's — the same number 1 is written every time.
  • Counting numbers — add 1 to the previous number.
  • Odd numbers — start at 1 and keep adding 2.
  • Even numbers — start at 2 and keep adding 2.
  • Triangular numbers — add 2, then 3, then 4, then 5, … (the amount added grows by one each time).
  • Squares — multiply a counting number by itself: 1×1, 2×2, 3×3, …
  • Cubes — multiply a counting number by itself three times: 1×1×1, 2×2×2, 3×3×3, …
  • Virahānka numbers — each number is the sum of the two numbers before it (2+3 = 5, 3+5 = 8, 5+8 = 13).
  • Powers of 2 — double the previous number.
  • Powers of 3 — multiply the previous number by 3.
Why it matters: once you can say the rule in words, you can continue the sequence as far as you like — you no longer need to remember the numbers.
Q2.
Rewrite each sequence of Table 1 in your notebook, along with the next three numbers in each sequence! After each sequence, write in your own words what is the rule for forming the numbers in the sequence.
Answer

The next three numbers of every sequence are shown in orange, and the rule is written beside it.

Number sequenceSequence given in Table 1Next three numbersRule in your own words
All 1's1, 1, 1, 1, 1, 1, 1, …1, 1, 1Every number is 1. Nothing ever changes.
Counting numbers1, 2, 3, 4, 5, 6, 7, …8, 9, 10Add 1 to the previous number.
Odd numbers1, 3, 5, 7, 9, 11, 13, …15, 17, 19Start at 1 and keep adding 2. These are the numbers not divisible by 2.
Even numbers2, 4, 6, 8, 10, 12, 14, …16, 18, 20Start at 2 and keep adding 2. These are the multiples of 2.
Triangular numbers1, 3, 6, 10, 15, 21, 28, …36, 45, 55Add 2, then 3, then 4, … The nth number is 1 + 2 + 3 + … + n.
Squares1, 4, 9, 16, 25, 36, 49, …64, 81, 100Multiply a counting number by itself: n × n.
Cubes1, 8, 27, 64, 125, 216, …343, 512, 729Multiply a counting number by itself three times: n × n × n.
Virahānka numbers1, 2, 3, 5, 8, 13, 21, …34, 55, 89Each number is the sum of the two numbers just before it.
Powers of 21, 2, 4, 8, 16, 32, 64, …128, 256, 512Double the previous number.
Powers of 31, 3, 9, 27, 81, 243, 729, …2187, 6561, 19683Multiply the previous number by 3.
Tip: To check a triangular number quickly, use Tn = n × (n + 1) ÷ 2. For example the 10th triangular number is 10 × 11 ÷ 2 = 55 — exactly what the pattern gives.
Was this helpful? Report an error