A DNA molecule with 220 base pairs length shows a pyrimidine to purine ratio of 1.2 on one strand. What will be the ratio of pyrimidine to purine on the second strand of DNA?

Pyrimidine/purine ratio on the first strand is 1.2/1 = 120/100.

So, in the first strand, out of every 220 bases, there are 120 pyrimidines and 100 purines.

 
Purine in one strand always pairs with pyrimidine in the other strand.

So, in the second strand, out of every 220 bases, there must be 100 pyrimidines and 120 purines.

Pyrimidine/purine ratio on the second strand must be 100/120 = 0.83.