Question

Solve:

$\left\{y|\frac{5y}{3}-7\le 13\right\}$, $y$ is a prime number

Answer 1

$\{y|\frac{5y}{3}-7\le 13\}$, y is a prime number

so $\frac{5y}{3}-7\le 13$

$\Rightarrow \frac{5y}{3}\le 13+7=20$

$\Rightarrow 5y\le 20\times 3=60$

$\Rightarrow y\le \frac{60}{5}=12$

so $y\le 12$ and y is a prime number.

so y can be $2,3,5,7,11$