Exercise No. 1D

NOTE: Answers to all questions are given at the end of this exercise.

Question No. 1:

Find the LCM of each of the following numbers.

(a) 3 and 7

(b) 6 and 9

(c) 7 and 21

(d) 12 and 9

(e) 24 and 18

(f) 65 and 135

(g) 100 and 75

(h) 144 and 36

(i) 250 and 125

(j) 63 and 490

 

Question No. 2:

Find the LCM of:

(a) 6, 9 and 15

(b) 14, 18 and 21

(c) 28, 44 and 68

(d) 65, 75 and 135

(e) 18, 12, 6 and 8

(f) 6, 12, 9 and 24

 

Question No. 3:

Find the LCM of each of the following pairs of numbers:

(a)  2² x 3³ x 5⁴ and 2 x 3⁴ x 5³ x 7

(b) 2³ x 3⁴ x 5 and 2² x 3⁴ x 5²

(c) 2² x 5 x 7 and 2³ x 3² x 5² x 11

 

Question No. 4:

Find the HCF and LCM of each of the following.

(a) 18 and 42

(b) 21 and 28

(c) 26 and 39

(d) 140 and 210

(e) 150 and 45

(f) 336 and 224

 

Question No. 5:

Two lighthouses flash their lights every 20 seconds and 30 seconds respectively. Given that they flash together at 8 p.m. when will they next flash together?

 

Question No. 6:

Three bells toll at intervals of 8 minutes, 15 minutes and 24 minutes respectively. If they toll together at 3 p.m., at what time will they next toll together?

 

Question No. 7:

David was trying to sleep one night but there was too much noise around him. His clock ticked every 5 seconds; a tap was dripping every 7 seconds and his pet dog snored every 12 seconds.

He noticed on his clock that all three things happened together on the stroke of midnight.

(a) After how many seconds would all three things happen together again?

(b) How many times would all three things happen together again between midnight and one o’clock?

 

Question No. 8:

Two cars start to drive around a 2-km track at the same time. Car X makes one lap every 80s, while car Y makes one lap every 60s.

(a) How long will it take  for the two cars to be at their starting position again? Give your answer in minutes.

(b) How long will it take the faster car to be ahead by 15 laps? Give your answer in hours.


Answers

(from left to right)

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