Question

Seven chits are numbered $1$ to $7.$ Four are drawn one by one with replacements. The probability that the least number on any selected chit is $5,$ is ${\left(\frac{a}{b}\right)}^c$ then $a+b+c$ is

Answer 1

$P($ or $6$ or $7)$ in one draw $=\frac{3}{7}$
$\therefore$ Probability that in each of $3$ draws, the chit bears $5$ or $6$ or $7={\left(\frac{3}{7}\right)}^3$