1 .
How many strings can be obtained by rearranging the letters of the word
BOOKKEEPER
(a)
${10 \choose 2} \cdot {8 \choose 2} \cdot {5 \choose 3} \cdot 3 \cdot 2$
(b)
$2! \cdot 2! \cdot 3!$
(c)
${10 \choose 2} \cdot {8 \choose 2} \cdot {6 \choose 3} \cdot {3 \choose 2}$
(d)
${10 \choose 2} \cdot {8 \choose 2} \cdot {6 \choose 3} \cdot 3 \cdot 2$