Real Numbers | Exercise 1.1

Question 5

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

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Solution

A number ending with 0 must have 2 and 5 as its prime factors.

Step 1 — Prime Factors of 6^n

Let's find the prime factors of the base number. The base number is 6. We can write 6 as a product of its prime factors.

6=2×36 = 2 \times 3

Now, let's find the prime factors of 6n6^n. We raise the prime factors to the power n.

6n=(2×3)n6^n = (2 \times 3)^n

=2n×3n= 2^n \times 3^n

6n=2n×3n\boxed{6^n = 2^n \times 3^n}

Step 2 — Checking for Factor 5

We use the Fundamental Theorem of Arithmetic. This theorem states that every composite number has a unique prime factorization. The prime factors of 6n6^n are 2 and 3. We can see that the prime factor 5 is not present. For 6n6^n to end with the digit 0, it must be divisible by 10. This means it must be divisible by both 2 and 5. Since 5 is not a prime factor of 6n6^n, 6n6^n is not divisible by 5. Therefore, 6n6^n cannot end with the digit 0.

Answer

6n6^n cannot end with the digit 0 for any natural number n.

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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