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Explanation:
For example, let's say we want to multiply 11 times 12.
We could decompose the 12 like this
11*12 = 11*(10+2) = 11*10+11*2 = 110+22 = 132
or we could decompose the 11 like this
11*12 = (10+1)*12 = 10*12+1*12 = 120+12 = 132
Either way, we see that 11*12 = 132
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In general, the distributive property says
a*(b+c) = a*b+a*c
which is the same as saying
(b+c)*a = b*a + c*a = a*b + a*c
This flip works because we can multiply in any order.