Question 1201505
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Venn Diagram template:
{{{
drawing(300,300,-5,5,-5,5,

line(-4,-3,-4,3),line(-4,3,4,3),line(4,3,4,-3),line(4,-3,-4,-3),

circle(1,0,2),circle(-1,0,2),

locate(-3.18,2.54,"volleyball"),locate(1.1,2.54,"basketball"),locate(-2.14,0.7,"a"),locate(-0.44,0.48,"b"),locate(1.42,0.76,"c"),locate(2.56,-1.86,"d")

)
}}}
region a = volleyball only
region b = both sports
region c = basketball only
region d = neither sport mentioned


I'll assume that d = 0, i.e. all of the players mentioned play either sport or both.


total = (number who play volleyball)+(number who play basketball) - (number who play both)
19 = (10)+(15) - (number who play both)
19 = 25 - (number who play both)
number who play both = 25-19
number who play both = 6
This value goes in region b.
{{{
drawing(300,300,-5,5,-5,5,

line(-4,-3,-4,3),line(-4,3,4,3),line(4,3,4,-3),line(4,-3,-4,-3),

circle(1,0,2),circle(-1,0,2),

locate(-3.18,2.54,"volleyball"),locate(1.1,2.54,"basketball"),locate(-2.14,0.7,"a"),locate(-0.44,0.48,"6"),locate(1.42,0.76,"c"),locate(2.56,-1.86,"0")

)
}}}
volleyball:
a+b = 10
a+6 = 10
a = 10-6
a = 4 who play volleyball only


basketball:
b+c = 15
6+c = 15
c = 15-6
c = 9 who play basketball only


This is what the completed Venn Diagram looks like
{{{
drawing(300,300,-5,5,-5,5,

line(-4,-3,-4,3),line(-4,3,4,3),line(4,3,4,-3),line(4,-3,-4,-3),

circle(1,0,2),circle(-1,0,2),

locate(-3.18,2.54,"volleyball"),locate(1.1,2.54,"basketball"),locate(-2.14,0.7,"4"),locate(-0.44,0.48,"6"),locate(1.42,0.76,"9"),locate(2.56,-1.86,"0")

)
}}}
</font>