Real Numbers | Exercise 1.1

Question 1

Express each number as a product of its prime factors:

(i) 140 (ii) 156 (iii) 3825 (iv) 5005 (v) 7429

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Solution

We will find the prime factors for each number.

Step 1 — Prime factors of 140

Let's divide 140 by prime numbers. We start with the smallest prime, 2.

140÷2=70140 \div 2 = 70

70÷2=3570 \div 2 = 35

35÷5=735 \div 5 = 7

7÷7=17 \div 7 = 1

140=2×2×5×7=22×5×7\boxed{140 = 2 \times 2 \times 5 \times 7 = 2^2 \times 5 \times 7}

Diagram 1

Step 2 — Prime factors of 156

Let's divide 156 by prime numbers. We start with the smallest prime, 2.

156÷2=78156 \div 2 = 78

78÷2=3978 \div 2 = 39

39÷3=1339 \div 3 = 13

13÷13=113 \div 13 = 1

156=2×2×3×13=22×3×13\boxed{156 = 2 \times 2 \times 3 \times 13 = 2^2 \times 3 \times 13}

Diagram 2

Step 3 — Prime factors of 3825

Let's divide 3825 by prime numbers. The sum of digits is 18, so it is divisible by 3.

3825÷3=12753825 \div 3 = 1275

1275÷3=4251275 \div 3 = 425

425÷5=85425 \div 5 = 85

85÷5=1785 \div 5 = 17

17÷17=117 \div 17 = 1

3825=3×3×5×5×17=32×52×17\boxed{3825 = 3 \times 3 \times 5 \times 5 \times 17 = 3^2 \times 5^2 \times 17}

Step 4 — Prime factors of 5005

Let's divide 5005 by prime numbers. The number ends in 5, so it is divisible by 5.

5005÷5=10015005 \div 5 = 1001

1001÷7=1431001 \div 7 = 143

143÷11=13143 \div 11 = 13

13÷13=113 \div 13 = 1

5005=5×7×11×13\boxed{5005 = 5 \times 7 \times 11 \times 13}

Step 5 — Prime factors of 7429

Let's divide 7429 by prime numbers. We try prime numbers like 17, 19, 23.

7429÷17=4377429 \div 17 = 437

437÷19=23437 \div 19 = 23

23÷23=123 \div 23 = 1

7429=17×19×23\boxed{7429 = 17 \times 19 \times 23}

Answer

(i) 140=22×5×7140 = 2^2 \times 5 \times 7 (ii) 156=22×3×13156 = 2^2 \times 3 \times 13 (iii) 3825=32×52×173825 = 3^2 \times 5^2 \times 17 (iv) 5005=5×7×11×135005 = 5 \times 7 \times 11 \times 13 (v) 7429=17×19×237429 = 17 \times 19 \times 23

More questions in Exercise 1.1

Q1

Express each number as a product of its prime factors:

(i) 140 (ii) 156 (iii) 3825 (iv) 5005 (v) 7429

Q2

Find the LCM and HCF of the following pairs of integers and verify that LCM × HCF = product of the two numbers.

(i) 26 and 91 (ii) 510 and 92 (iii) 336 and 54

Q3

Find the LCM and HCF of the following integers by applying the prime factorisation method.

(i) 12, 15 and 21 (ii) 17, 23 and 29 (iii) 8, 9 and 25

Q4

Given that HCF (306, 657) = 9, find LCM (306, 657).

Q5

Check whether 6n6^n can end with the digit 0 for any natural number nn.

Q6

Explain why 7×11×13+137 \times 11 \times 13 + 13 and 7×6×5×4×3×2×1+57 \times 6 \times 5 \times 4 \times 3 \times 2 \times 1 + 5 are composite numbers.

Q7

There is a circular path around a sports field. Sonia takes 18 minutes to drive one round of the field, while Ravi takes 12 minutes for the same. Suppose they both start at the same point and at the same time, and go in the same direction. After how many minutes will they meet again at the starting point?

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