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Understanding
O Draw a factor tree for each of the following numbers.
a) 36 b) 72 c) 80
Q Work out the product and write them using exponents,
a) 2x2x2x3x3x5x5 b) 2x2x3X5x5
How to use factor trees to find the LCM
Drawing the factor tree to find the LCM of 120 and 45
: 120
Draw the factor tree Write the number of 120 Repeat the process for the Write the number of
for number 120. as the product of its prime other number, that is 45. 45 as the product of
numbers. its prime numbers.
120 = 2X2X2X3X5 45 = 3 X 3 X 5
= 23 X 3 X 5 = 32 X 5
The LCM of 120 and 45 is the product of the
largest multiple of each prime that appears 120 = 2^ x 3 X 5 Spotlight
on one of the factor trees. 45 = 3^ x 5 O
• Prime factor 2 which appears three times: 7}
Try growing a
• Prime factor 3 which appears twice: 3^
factorisation forest!
• Prime factor 5 which appears once: 5
h
LCM of 120 and 45 = 2^ x 3^ x 5
=2x2x2x3x3x5
=8x9x5
= 360
Therefore the LCM of 120 and 45 is 360.
o
