Question

There are five types of envelopes and four types of stamps in a post office. how many ways are there to buy an envelope and a stamp?

Answer 1

Answer:

20

Step-by-step explanation:

Total no. of envelopes = 5

Total no. of stamps = 4

We need to choose 1 envelope and 1 stamp

So, we will use combination over here to find the possible no. of ways

Formula : $^nC_r=\frac{n!}{r!(n-r)!}$

No. of possible ways to buy an envelope and a stamp= $^5C_1 \times ^4C_1$

                                                                                         = $\frac{5!}{1!(5-1)!}\times \frac{4!}{1!(4-1)!}$

                                                                                         = $\frac{5!}{1!(4)!}\times \frac{4!}{1!(3)!}$

                                                                                         = $5\times 4$

                                                                                         = $20$

Hence  No. of possible ways to buy an envelope and a stamp is 20