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Question (31)

QN0030503

Find the LCM of 45 and 54.

(A) 90
(B) 180
(C) 270
(D) 540

Correct Answer: C

Explanation:

45 = 3² × 5 and 54 = 2 × 3³. LCM = 2 × 3³ × 5 = 270.

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Question (32)

QN0030504

Which statement is true while finding the LCM using prime factorisation?

(A) Ignore the prime factors that are not common.
(B) Take only the smallest prime factor.
(C) Include every prime factor with its greatest occurrence in the given numbers.
(D) Include only the common prime factors.

Correct Answer: C

Explanation:

The LCM is obtained by taking all prime factors with their maximum occurrences.

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Question (33)

QN0030505

Find the LCM of 36 and 54.

(A) 72
(B) 96
(C) 108
(D) 216

Correct Answer: C

Explanation:

36 = 2² × 3² and 54 = 2 × 3³. LCM = 2² × 3³ = 108.

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Question (34)

QN0030506

A red light flashes every 20 seconds and a green light flashes every 30 seconds. If both flash together now, after how many seconds will they flash together again?

(A) 40
(B) 50
(C) 60
(D) 120

Correct Answer: C

Explanation:

LCM of 20 and 30 is 60 seconds.

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Question (35)

QN0030507

Find the LCM of 42 and 70.

(A) 140
(B) 210
(C) 280
(D) 420

Correct Answer: B

Explanation:

42 = 2 × 3 × 7 and 70 = 2 × 5 × 7. LCM = 2 × 3 × 5 × 7 = 210.

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Question (36)

QN0030508

The LCM of 16, 20 and 40 is:

(A) 40
(B) 80
(C) 160
(D) 320

Correct Answer: B

Explanation:

LCM = 2⁴ × 5 = 80.

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Question (37)

QN0030509

The prime factorisations of two numbers are: 72 = 2³ × 3² 90 = 2 × 3² × 5 The LCM is:

(A) 180
(B) 240
(C) 360
(D) 720

Correct Answer: C

Explanation:

LCM = 2³ × 3² × 5 = 360.

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Question (38)

QN0030510

Three bells ring after every 4 minutes, 6 minutes and 8 minutes respectively. If they ring together now, after how many minutes will they ring together again?

(A) 12
(B) 18
(C) 24
(D) 48

Correct Answer: C

Explanation:

LCM of 4, 6 and 8 is 24 minutes.

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Question (39)

QN0030511

Find the LCM of 56 and 72.

(A) 252
(B) 360
(C) 504
(D) 1008

Correct Answer: C

Explanation:

56 = 2³ × 7 and 72 = 2³ × 3². LCM = 2³ × 3² × 7 = 504.

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Question (40)

QN0030512

A factory inspects one machine every 15 days and another every 25 days. If both machines are inspected today, after how many days will they next be inspected together?

(A) 50
(B) 60
(C) 75
(D) 150

Correct Answer: C

Explanation:

LCM of 15 and 25 is 75 days.

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Question (31)

Find the LCM of 45 and 54.

Explanation:

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Question (32)

Which statement is true while finding the LCM using prime factorisation?

Explanation:

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Question (33)

Find the LCM of 36 and 54.

Explanation:

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Question (34)

A red light flashes every 20 seconds and a green light flashes every 30 seconds. If both flash together now, after how many seconds will they flash together again?

Explanation:

Link:

Question (35)

Find the LCM of 42 and 70.

Explanation:

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Question (36)

The LCM of 16, 20 and 40 is:

Explanation:

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Question (37)

The prime factorisations of two numbers are: 72 = 2³ × 3² 90 = 2 × 3² × 5 The LCM is:

Explanation:

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Question (38)

Three bells ring after every 4 minutes, 6 minutes and 8 minutes respectively. If they ring together now, after how many minutes will they ring together again?

Explanation:

Link:

Question (39)

Find the LCM of 56 and 72.

Explanation:

Link:

Question (40)

A factory inspects one machine every 15 days and another every 25 days. If both machines are inspected today, after how many days will they next be inspected together?

Explanation:

Link:

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