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Problem
Problem
Find the positive number of solutions of
x
+
y
+
z
+
w
=
20
x+y+z+w=20
x
+
y
+
z
+
w
=
20
under the following conditions a. Zero value of
x
,
y
,
z
x, y, z
x
,
y
,
z
and
w
w
w
are included. b. Zero values are excluded.
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