Venn diagrams: how many only watched tv1

In a poll 98 persons said that they watched Tv1, 76 watched Tv2, 83 watched tv3, 30 both Tv1 and Tv2, 35 watched Tv2 and Tv3, 20 watched Tv1 and Tv3 and finally 17 watched all the three channels. How many ONLY watched Tv1?

Thanks for the help!

For any category C, let N(C) denote the number of people in category C.

We have
N(Tv1 only) + N(Tv1 and Tv2 only) + N(Tv1 and Tv3 only) + N(Tv1 and Tv2 and Tv3) = N(Tv1)

N(Tv1 and Tv2 only) + N(Tv1 and Tv2 and Tv3) = N(Tv1 and Tv2)
N(Tv1 and Tv3 only) + N(Tv1 and Tv2 and Tv3) = N(Tv1 and Tv3).

Therefore,

N(Tv1 only) = N(Tv1) - N(Tv1 and Tv2 only) - N(Tv1 and Tv3 only) - N(Tv1 and Tv2 and Tv3)

= N(Tv1) - [N(Tv1 and Tv2) - N(Tv1 and Tv2 and Tv3)] - [N(Tv1 and Tv3) - N(Tv1 and Tv2 and Tv3)] - N(Tv1 and Tv2 and Tv3)

= 98 - (30 - 17) - (20 - 17) - 17
= 65.

So 65 people only watched Tv1.

May Jesus richly bless you today!