There are 20 x 1/2 = <<20*1/2=10>>10 red roses in each row.
So there are 20 - 10 = <<20-10=10>>10 roses that are not red in each row.
Out of the 10 remaining roses in each row, 10 x 3/5 = <<10*3/5=6>>6 roses are white.
Thus, there are 10 - 6 = <<10-6=4>>4 pink roses in each row.
Therefore, Mrs. Dawson has 4 pink roses each in 10 rows for a total of 4 x 10 = <<4*10=40>>40 pink roses in her rose garden.
#### 40