8 Answers
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720
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10 x 9 x 8 = 720
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'!' mean factorial
10! means you multiply 10 X 9 X 8 X 7... X 1
and
7! means 7 X6 X 5 ... X 1
so, when you have factorials like this, you can look at them as
10 X 9 X 8 X 7!
divided by
7!
now you can cleanly factor out the 7! from the top and bottom and all you have to compute is 10 X 9 X 8.
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Make the fractions mistaken 10 x 28 + 9 = 289/10 10 x 7 + 7 = seventy seven/10 seeing that they have the comparable denominator, upload the numerators 366/10 Simplify (divide numerator via denominator) 36 6/10
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Factorials are not as difficult once you recognize and apply n! = n*(n-1)! or 10! = 10*9! Using that same principal 10! = 10*9*8*7!
so you have 10*9*8*7!/7! = 10*9*8= 720
The neat thing about this concept that it works with even very large numbers such as 52!/50! = 52 *51 = 2652
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10! / 7! = (10*9*8*7!) / 7! = 10*9*8 = 720
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10!/7!=10x9x8x7! / 7! = 10x9x8 = 720
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Factorialize both numbers, and divide.