1-(1/160) is greater because 1/160 is smaller than 1/120.

Correct !

Also, think about it this way

1- (1/160) = 159/160

and

1-(1/120) = 119/120

Now,

1. 119/120 is less than 1
2. If we add 40 to both numerator and denominator of 119/120 we get

(119 + 40) / (120 +40) = 159/160.


As a general rule, if a fraction is less than 1 and if we add the same positive number to the numerator and denominator. The value of the fraction increases, as its going closer to 1.

So, 159/160 is greater than 119/120.


Also, note : if the fraction compare was 120/119 vs 160/159,
120/119 would be greater.