Three interlocking circles represent the three media sets. Label them N (newspapers), T (television), R (radio). The people surveyed is a larger circle completely enclosing the others. There are 8 separate regions, caused by the interlocking circles and the region between the interlocking circles and the large surrounding circle.
a. N only
b. T only
c. R only
d. N and T only
e. T and R only
f. N and R only
g. All 3
h. None
Radio set: cefg=340; TV set: bdeg=150; newspaper set: adfg=180; N&R: fg=80; N&T: dg=85; R&T: eg=35; none: h=25. (cefg means c+e+f+g, etc., the total of the numbers of people in the regions.)
From these:
abcdefg=520-25=495; ad=100; af=95; be=65; ce=260; bd=115; c=495-adbefg=495-245=250; e=10; b=55; g=25; d=60; a=40; f=55. So (a,b,c,d,e,f,g)=(40,55,250,60,10,55,25,25). Therefore, g=25 is the number using all 3 sources.