counting principle (5m)

用戶90882

2010-08-06 5:05 am

Knowledge: addition rule / multiplication rule in the counting principle

Question: David is shopping for DVDs. There are 3 types of DVDs available in a shop, including local movies, foreign movies and music albums. David is interested in DVDs from 3 local movies, 5 foreign movies and 2 music albums. In each of the following conditions, how many choices does he have?

(a) Buying one of the DVDs.
(b) Buying two of the DVDs of different types.

Solutions: (a) 10 (b) 31

I know (a). But I don't know (b).
(a) No. of choices required = 3 + 5 + 2 = 10 choices

Please show steps and explain the steps in details. Thank you. 5 marks

回答 (1)

用戶9112

2010-08-06 5:35 am

✔ 最佳答案

For 2 different types of DVDs, he can buy a local movie and a foreign movie, there are 3*5=15 waysa local movie and a music album, there are 3*2=6 waysa foreign movie and a music album, there are 5*2 =10waysAll in all, there are 15+6+10=31 ways

👍 0 👎 0