The World of Numbers | Exercise 3.1

Question 2

Look at the sequence of numbers on one column of the Ishango bone: 11, 13, 17, 19. What do these numbers have in common? List the next three numbers that fit this pattern.

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Solution

Let's find the common property of the given numbers and then list the next three numbers.

Step 1 — Identify the pattern

We are given the numbers 11, 13, 17, 19. Let's check if these numbers are prime. A prime number has only two factors: 1 and itself.

Factors of 11:1,11\text{Factors of } 11: 1, 11 Factors of 13:1,13\text{Factors of } 13: 1, 13 Factors of 17:1,17\text{Factors of } 17: 1, 17 Factors of 19:1,19\text{Factors of } 19: 1, 19

All the given numbers are prime numbers.\boxed{\text{All the given numbers are prime numbers.}}

Step 2 — Find the next three numbers

We need to find the next three prime numbers after 19. Let's list numbers starting from 20 and check if they are prime.

20 is not prime (divisible by 2,4,5,10).20 \text{ is not prime (divisible by } 2, 4, 5, 10). 21 is not prime (divisible by 3,7).21 \text{ is not prime (divisible by } 3, 7). 22 is not prime (divisible by 2,11).22 \text{ is not prime (divisible by } 2, 11). 23 is prime (divisible only by 1,23).23 \text{ is prime (divisible only by } 1, 23). 24 is not prime.24 \text{ is not prime.} 25 is not prime.25 \text{ is not prime.} 26 is not prime.26 \text{ is not prime.} 27 is not prime.27 \text{ is not prime.} 28 is not prime.28 \text{ is not prime.} 29 is prime (divisible only by 1,29).29 \text{ is prime (divisible only by } 1, 29). 30 is not prime.30 \text{ is not prime.} 31 is prime (divisible only by 1,31).31 \text{ is prime (divisible only by } 1, 31).

The next three prime numbers are 23,29,31.\boxed{\text{The next three prime numbers are } 23, 29, 31.}

Answer

(i) The numbers 11, 13, 17, 19 are all prime numbers. (ii) The next three numbers that fit this pattern are 23, 29, 31.

More questions in Exercise 3.1

Q1

A merchant in the port city of Lothal is exchanging bags of spices for copper ingots. He receives 15 ingots for every 2 bags of spices. If he brings 12 bags of spices to the market, how many copper ingots will he leave with?

Q2

Look at the sequence of numbers on one column of the Ishango bone: 11, 13, 17, 19. What do these numbers have in common? List the next three numbers that fit this pattern.

Q3

We know that Natural Numbers are closed under addition (the sum of any two natural numbers is always a natural number). Are they closed under subtraction? Provide a couple of examples to justify your answer.

Q4

Ancient Indians used the joints of their fingers to count, a practice still seen today. Each finger has 3 joints, and the thumb is used to count them. How many can you count on one hand? How does this relate to the ancient base-12 counting systems?

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