A Detailed solution here would be -
using the following concept -
https://gre.myprepclub.com/forum/gre-quant-overlapping-set-theory-18835.html#p54150Assuming you've grasped the above concept very well. Draw a basic venn diagram and do diagrammatic notation on it as well. I have added a rough venn diagram for reference.
We have been given.
a = 9 ---- (eq1)
b = 10 ---- (eq2)
c = 11 ---- (eq3)
d + g +e = 40 ---- (eq4)
f + g+ e = 49 ---- (eq5)
f + d + g = 31 ---- (eq6)
g = 20 ---- (eq7)
And, we need to find 'f' from these.
Now, add equation 4,5,6
you get 2*(f + e + d) + 3g = 120.
Which gives you f + e +d = 60 ---- (eq8)
Now, use eq (8,7,6) and get the value of f which comes out to be = 10
Thanks
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