Question

Seven chits are numbered from 1 to 7. Four are drawn one by one with replacement. The probability that the least number on any selected chit is 5 is

• A. $1-(\frac{2}{7}{)}^4$
• B. $4-(\frac{2}{7}{)}^4$
• C. $(\frac{3}{7}{)}^4-(\frac{2}{7}{)}^4$
• D. $(\frac{3}{7}{)}^4$

Answer 1

The correct option is D $(\frac{3}{7}{)}^4$

The total number of choices I have at any given instant is 7 since the chits are replaced every time.
The allowed choices for the given condition are 5, 6, 7 i.e. I have only 3 favored choices.
Hence, $\frac{3^4}{7^4}$