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4. The HCF of the numbers 10, 15 and 20 is .................... .

5. The smallest odd composite number having two digits is .................... .
D. State whether the following statements are True (T) or False (F).
1. 81 is a prime number.

2. Every number is a multiple of itself.
3. Every number is the smallest factor of itself.

4. Every composite number has more than two factors.
5. Two consecutive numbers that differ by 2 are called twin primes.
E. Solve the following questions.

1. Write all prime numbers between 40 and 100.
2. Express each of the following numbers as the sum of two odd primes.

(a) 44 (b) 50 (c) 64 (d) 88
3. Express each of the following numbers as the sum of three odd primes.
(a) 63 (b) 79 (c) 15 (d) 31

4. Find the common factors of
(a) 60, 75 and 120 (b) 72, 80 and 90 (c) 18, 24 and 30

5. Find the first five common multiples of
(a) 2, 3, 5 (b) 3, 4, 5 (c) 5, 7 (d) 8, 12, 15
6. Factorise each of the following using the factor tree method.

(a) 24 (b) 364 (c) 1000 (d) 162
7. Find the sum of the factors that will be put in the missing places.

60
? ?
10 3

? 2

8. Find the pair of prime numbers less than a hundred having the same digits.
9. If * is the 8th prime number and # is the 11th prime number then what is the value of # – *?
10. What is the least value that should be given to * so that the number 653*47 is divisible by 11?

11. There are 72 green coloured, 144 red coloured and 234 orange coloured chairs in an auditorium.
A boy wants to put the chairs in rows such that each row is of the same coloured chairs and the
number of chairs is equal in each row.

(a) What is the greatest number of chairs in each row?
(b) Also, find the minimum number of rows of chairs in the auditorium.

CompetenCy Based Question

12. If * and # are the two digits of the number 653*# such that this number is divisible by 80 then what
will be the minimum value of * + #? CompetenCy Based Question

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