#### Answer

Marginal distribution is the sum of counts of each column divided by sample size of 1808
As & Bs = $\frac{736+205}{1808} = 0.5205 = 52.05%$
Cs = $\frac{450+144}{1808} = 0.3285 = 32.85%$
Ds & Fs = $\frac{193 + 80}{1808} = 0.1510 = 15.10%$
From this we can deduce that 32.85% + 15.10% = 47.95% of students received a Grade C or lower

#### Work Step by Step

As given above