Page 69 - ICSE Math 6

(e) 4, 7 and 13 are prime numbers. (f) 13, 19 and 89 are prime numbers.
(g) 10 and 33 are co-prime numbers. (h) 2 and 3 are the prime factors of 10.

(i) 5 and 7 are the prime factors of 35. (j) There are finite multiples of 13.
2. For any two numbers, their LCM is divisible by:

(a) one of the numbers (b) both the numbers (c) none of the numbers

PRACTICE TIME

1. Find all the factors of the following numbers.
(a) 33 (b) 22 (c) 122 (d) 175 (e) 300

2. Sort out the prime numbers, co-prime numbers and the composite numbers from 3, 12, 15, 70
and 112.
3. Find all the prime numbers between 20 and 40.
4. Find the HCF of the following numbers.
(a) 12 and 18 (b) 91 and 49 (c) 45, 75 and 135

(d) 96, 72 and 128 (e) 40, 60 and 100 (f) 120, 80, 20 and 140
5. Find the greatest number that will divide 36, 27 and 45 exactly.

6. Find the greatest number that will divide 21, 27 and 29 leaving the remainder 1 in each case.
7. Write the following.
(a) First four multiples of 13 (b) First five multiples of 9
(c) First five multiples of 15 (d) First six multiples of 8

8. Find the LCM of the following numbers.
(a) 6 and 8 (b) 12 and 18 (c) 21, 45 and 63
(d) 100, 150 and 200 (e) 48, 60 and 120 (f) 12, 18, 24 and 36

9. Find the smallest number which is exactly divisible by 135, 162 and 324.
10. Find the smallest number which when divided by 24, 36, 54 and 60 leaves 6 as the remainder in
each case.
11. Find the least number which is exactly divisible by 28, 42, 84 and 36 when:
(a) decreased by 2 (b) increased by 7

12. The HCF and LCM of two numbers is 1 and 342 respectively. If the smaller number is 18, find
the bigger number.
13. The HCF of 26 and 455 is 13. Find their LCM.
14. Find the LCM of 105 and 175. Use this to find their HCF.

15. Verify the relation between HCF and LCM of 222 and 125.
16. There are 24, 28 and 30 students in three different sections of class VI. A teacher wants to divide
all of them in different groups such that each group has equal number of students from each
section. What is the maximum number of groups into which the students can be divided?
th
17. During a festive season, every 5 customer of an online electronic store gets free delivery and
th
every 9 customer earns discount coupons for the next purchase. Who will be the first customer
to get free delivery as well as discount coupons?

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