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E:\Working\Focus_Learning\Math_Genius_5_(05-10-2023)\Open_Files\CHAP_03
\\February 16, 2024 2:20 PM Surender Prajapati Proof 5 Reader _________________________ Date: ___________________74

Solution: (a) 2 20, 60, 90 (b) 2 24, 40, 72
2 10, 30 45 2 12, 20, 36
3 5, 15, 45 2 6, 10, 18
5 5, 5, 15 3 3, 5, 9
3
3 1, 5,
3 1, 1, 3 5 1, 5, 1
1, 1, 1 1, 1, 1

LCM = 2 × 2 × 3 × 3 × 5 LCM = 2 × 2 × 2 × 3 × 3 × 5
= 180 = 360

Practice time 3F

1. Write the common multiples of each pair of numbers. Circle their smallest common
multiple.

(a) 12, 20 (b) 16, 24 (c) 14, 21 (d) 18, 30 (e) 10, 15

2. Find the LCM of these numbers using the common multiples method.

(a) 21, 28 (b) 48, 72 (c) 22, 110 (d) 60, 63

(e) 24, 36 (f) 38, 57 (g) 12, 15, 18 (h) 20, 30, 50

(i) 20, 32, 40 (j) 11, 22, 33 (k) 12, 15, 40 (l) 12, 16, 32

3. Find the LCM of these numbers using the prime factorisation method.

(a) 14, 17 (b) 51, 54 (c) 78, 82 (d) 25, 75

(e) 54, 90 (f) 24, 72 (g) 18, 20, 32 (h) 12, 16, 30

(i) 21, 24, 36 (j) 3, 15, 60 (k) 33, 55, 99 (l) 12, 18, 24

4. Find the LCM of these numbers using the division method.

(a) 4, 24, 32 (b) 24, 42, 72 (c) 20, 60, 90 (d) 18, 36, 48

(e) 9, 13, 26 (f) 18, 9, 27 (g) 32, 16, 50 (h) 14, 35, 49

5. two bulbs flash at regular intervals of 42 and 77 seconds respectively. they first
flash together at 10:45 p.m. At what time will they flash together:

(a) Second time? (b) Fifth time?

6. Sia has a collection of hair bands and she wants to arrange them in groups of 4, 6 or
8 with no hair band left behind. Find the number of hair bands she has.

7. Two bells ring at intervals of 24 min and 36 min respectively. If they ring at 8:15 a.m.,
when will they ring together next?

74 Mathematics-5