Prove that     n C r + n C r-1 =  n+1 C r

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nathanshields | High School Teacher | (Level 1) Associate Educator

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Hi - looking at these equations can be a little confusing, so just take them one at a time, writing down each step to make sure you understand.



Adding them together requires a common denominator, which can be r!(n-r+1)!






Cha-ching!  This is what we wanted! ```(n+1)C(r)`


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