Two coins are tossed simultaneously 500 times, and we get
two heads : 105 times
one head : 275 times
no head : 120 times
find the probability of occurrence of each of these events.

The probability of 2 heads:
105:500

This can be simplified further. If you divide them both by 5, you get:

21:100

That is the answer, as it cannot be simplified any further.

The probability of one head:
275:500

This can be simplified further. If you divide them both by 25, you get:

11:20

That is the answer, as it cannot be simplified any further.

The probability of no heads:
120:500

This can be simplified further. If you divide them both by 20 you get:

6:25

That is the answer, as it cannot be simplified any further.

So:
a) 21:100
b) 11:20
c) 6:25

Yes, two vertical lines can be complementary