The number of positive integer solutions for the equation x +y +z + t = 21 is	Select the correct option
A) 1140
B) 1145
C) 1240
D) 1340
E) 15640
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.   21-1 C 4-1 = 20C3 = 1140   1140nswer : 1140
<result>A</result>
The number of positive integer solutions for the equation x +y +z + t = 21 is