Conceptual wayAs a general strategy in basic Question on Permutation Combination like this we
first arrange the letters on which there is a condition and then arrange the
remaining letters.
So out of the five positions where the 5 letters needs to be arranged we will first
arrange letters P and R.
So letters P and R will take two positions so lets select two positions out of 5
positions where letters P and R will be placed
Two positions can be selected out of 5 positions in 5C2 ways = 10 ways.
Once two positions have been selected we know P will be in the left position and
R will be in right so there is only one way we can place letters P and R in these
two positions.
And the remaining 3 letters can be placed in 3 posions in 3! Ways = 6 ways.
So the final Answer = number of ways letters P and R can be arranged x number
of ways the other 3 letters can be arranged
Final Answer = 10 x 6 = 60 ways
JAMBOREE Way Now 5 letters can be placed in 5 positions in 5! Ways = 120.
Logically we can analyze that either letter P will be to the left of letter R or to the
right of letter R.
So by simple reasoning we will get that in half of the ways letter P will be to the
left of letter R.
So the correct answer = ½ total number of ways
= 60 ways
We make the
GMAT simple!
_________________
Aryama Dutta Saikia
Jamboree Education Pvt. Ltd.