Practice Set 12
1. Find the HCE
(1) 25, 40 (ii) 56, 32 (iii) 40, 60, 75 (iv) 16, 27
() 18, 32, 48 (vi) 105, 154 (vii) 42, 45, 48 (viii) 57, 75, 102
(ix) 56, 57 (x) 777, 315, 588
2. Find the HCF by the division method and reduce to the simplest form,
275
76
161
(ii)
(iii)
133
69
(1) 525
Let's recall.
Least Common Multiple (LCM)
The Least Common Multiple of the given numbers is the smallest number that is
divisible by each of the given numbers.
• Write the tables of the given numbers and find their LCM.
(i) 6,7 (ii) 8, 12 (iii) 5, 6, 15
19
Answers
Answer:
Question 1:
Which number is neither a prime number nor a composite number?
ANSWER:
1 is neither a prime number nor a composite number.
Page No 15:
Question 2:
Which of the following are pairs of co-primes?
(i) 8, 14
(ii) 4, 5
(iii) 17, 19
(iv) 27, 15
ANSWER:
Two numbers which have only 1 as a common factor are said to be co-prime or relatively prime or mutually prime numbers.
We can write 17 as 17 × 1 and 19 as 17 × 1.
Hence, 17 and 19 is a pair of co-prime numbers.
Page No 15:
Question 3:
List the prime numbers from 25 to 100 and say how many they are.
ANSWER:
There are a total of 16 prime numbers between 25 and 100 which are 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97.
Page No 15:
Question 4:
Write all the twin prime numbers from 51 to 100.
ANSWER:
If the difference between two co-prime numbers is 2, the numbers are said to be twin prime numbers.
Hence, the twin prime numbers between 51 and 100 are 59 and 61, 71 and 73.
Page No 15:
Question 5:
Write 5 pairs of twin prime numbers from 1 to 50.
ANSWER:
If the difference between two co-prime numbers is 2 then, the numbers are said to be twin prime numbers.
Hence, the twin prime numbers from 1 to 50 are (2,3), (5,7), (11,12), (17,19) and (29,30).
Page No 15:
Question 6:
Which are the even prime numbers?
ANSWER:
There is only even prime number which is 2.
Explanation:
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