Question

Number of ways of selection of 4 letters of the word "PERFECT" is

• A. 15
• B. 21
• C. 25
• D. 31

Answer 1

Answer: (C)

7 letters
$P\to 1$
$E\to 2$
$R\to 1$
$F\to 1$
$C\to 1$
$T\to 1$
$2\text{ alike }+2\text{ diff. }=1\times {}^5{C}_2=10$
$\text{ All }4\text{ different }={}^6{C}_4=15\Rightarrow 25$