Someone
what is the coefficient of x^6y^4 in the expansion of (x+y)^10
a.1
b.5
c.210
d. it does not exist

Looking at Pascal's Triangle, specifically at the row that starts with 1, 10, etc we see the value 210 in the 4th slot (start the count at 0) since 10-6 = 4

Or you can use the combination formula nCr to get the same result

nCr = (n!)/(r!*(n-r)!)
10C4 = (10!)/(4!(10-4)!)
10C4 = (10!)/(4!*6!)
10C4 = (10*9*8*7*6!)/(4!*6!)
10C4 = (10*9*8*7)/(4!)
10C4 = (10*9*8*7)/(4*3*2*1)
10C4 = 210

Either way, the final answer is Choice C) 210