My posts on Permutation and combination begins from today. After serious thoughts, I concluded that the best way to go about P & C is to proceed question by question approach. I will post questions and P&C daily and while explaining the OA I will try to explain the basic concepts and fundas. The best way to start is to start simple
Let's get started than
Mr. X has come to a garment store to buy dress. Store has 20 trousers and 30 shirts. In how many ways he can buy
1) 1 shirt and 1 trouser
2) only one garment out of these
Post your solution and also let me know if you have any problem in approaching this problem
Thanks,
Quant-Master
Posts
Response to question 1:
ReplyDeleteHere the question is to select one shirt AND one trouser. Please note that whenever you have AND in the problem we multiply both the selection.
I can select 1 shirt out of 30 in 30c1 = 30 ways
I can select 1 trouser out of 20 in 20c1 = 20 ways
Now we multiply the selection of shirts and trousers = 30*20 = 600.
Note: you need not calculate 30c1 or 20c1 everytime, when selection is this simple. For example if you have to select 1 out of 2 shirts, you select either 1st or 2nd shirt---2 ways. Similary if you have 3 shirts you select either 1 or 2 or 3 ---3 ways. Similarly out of 30 you will select 1 or 2 or 3 or...30 which is 30 ways.
Response to question 2:
Here you are selecting only one garment out of 30 shirts and 20 trousers. You can select either shirts OR trousers.
You can select 1 out of 30 shirts in 30 ways
OR
You can select 1 out of 20 trousers in 20 ways
Henec selecting one garment is 30+20=50
Here is the more simpler way:
Since you have to select one garment out of 30 shirts and 20 trousers. Total garments available for selection is 50. Out of this 50 you can select one in 50 ways.
Let me know if you have any queries. Also post any specific queries you have in permutation & combination and if you feel I should change my teaching approach in P&C let me know.
Thanks,
Quant-Master
That was a good explanaiton. I get confused with slightly tougher questions. Looking forwad to your explaining the tougher ones...Thanks
ReplyDelete