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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