The number of positive integer solutions for the equation x +y +z + t = 18 is	Pick.
A) 640  B) 780  C) 380  D) 540  E) 680
The number of positive integer solutions for the equatio fx1+x2+⋯+xn=k   (k-1)C(n-1)- where k is the number and n is number of variable in the equation.   18-1 C 4-1 = 17C3 = 680   Answer : 680
<result>E</result>
The number of positive integer solutions for the equation x +y +z + t = 18 is