Answer
$\frac{3}{5}$
Work Step by Step
We know that $probability=\frac{\text{number of favourable outcomes}}{\text{number of all outcomes}}$
The total number of students (the number of all outcomes) is $350$
By using the table, there are $50$ high income and $160$ middle income families, thus there are $50+160=210$ "good outcomes".
Hence the probability here is: $\frac{210}{350}=\frac{3}{5}$