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BAT write a number as a product of primes BAT Find the LCM of two numbers

LCM 1 Daniel is going to put all his marbles into groups of size 20 or 12 only What is the smallest number of marbles that Daniel could have if he has more than 12 marbles? Discuss: Start with answers made of 8s and 12s like 20 = 8 + 12, 24 = 3x8 or 12x2, 32 = 2x12 + 8 … Then say we only want numbers that are in BOTH x tables e.g. 24, … how many can you find? Q – next answer after 24? = 48, then 72 … Explain 24 is the Lowest common multiple LCM or leave this until example III Discuss definition of LCM– lowest number in both times tables …

LCM 2 Two lighthouses can be seen from the top of a hill. The first flashes once every 36 seconds, and the other flashes once every 54 seconds. If they flash at the same time, how long will it be until they flash at the same time again?

LCM 3 Westcliff primary is going to put all its students next year into classes of size 16 or 22 only (not both) What is the smallest number of students over 22 that could be on next years roll at Westcliff? Answer = 176 (2x2x2x2x11)

The school bell sounds every 90 minutes. LCM 4 The school bell sounds every 90 minutes. The school buzzer sounds every 150 minutes Both bell and buzzer sound at 9:00 am What is the next time at which both will sound together? Answer 4:30 pm 450 minutes forward as 450 is the LCM of 90 and 150

Tom, Sam and Matt are counting drum beats. LCM 5 Tom, Sam and Matt are counting drum beats. Tom hits a snare drum every 2 beats. Sam hits a kettle drum every 5 beats. Matt hits a bass drum every 8 beats. Tom, Sam and Matt start by hitting their drums at the same time. How many beats is it before Tom, Sam and Matt next hit their drums at the same time? Find LCM of 2 5 and 8 LCM of 2 5 and 8 = 40 It is 40 beats before they next hit their drums at the same time.

TRY THESE: Find the LCM MODEST ONES TRICKIER ONES 24 and 40 42 and 63 44 and 242 24 and 60 48 and 60 66 and 48 56 and 35 42 and 54 70 and 175 35 and 75 50 and 70 240 and 540 28 and 48 75 and 105 20 and 56 42 and 98 Answers:

BAT write a number as a product of primes Summary You should be able to: BAT write a number as a product of primes BAT Find the LCM of two numbers One thing I have learned is … One thing I can improve is …

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