The nitrogenous bases in a DNA are Purines – Adenine, Guanine and Pyrimidines – Cytosine ,Thymine. A purine pairs with Pyrimidine.
A=T
C = G
According to Chargaff’s Rule, in DNA, the amount of adenine equals the amount of thymine and the amount of guanine equals the amount of cytosine.
If c=550, G will also be 550. C+G = 550+550=1100.
thus , A+T = 1500 – 1100 = 400.
A= T
so A= 400/2 = 200
T= 400/2=200.
Purines are A and G
A= 200
G= 550
therefore A+G = 200+550=750