The Postage Stamp Problem

[baileygirl76]

Imagine that the post office only sold stamps in 5-cen and 7-cent denomiations. What amounts of postage could you buy, and wht amounts could you not buy?

Any help would be great. I am hoping someone can explain how to do this problem.

Thanks!

Melissa

 

[Deleted member 4993]

Imagine that the post office only sold stamps in 5-cen and 7-cent denomiations. What amounts of postage could you buy, and wht amounts could you not buy?

Any help would be great. I am hoping someone can explain how to do this problem.

Thanks!

Melissa

You can immediately see that you cannot buy a 6 cent stamp - what else....

Please show us your work, indicating exactly where you are stuck so that we may know where to begin to help you.

 

[baileygirl76]

I have been working on it more and think that I have figured out that you can buy 5,7,10,12,14,15,17,19,20,21,22 cents worth of stamps and then anything 24 cents and higher. The only ones you can't buy are 1-4, 6,8,9,11,13,16,18,23 cent stamps. Is this correct? I had to just guess and check. Is there an easier way to figure it out?

Thanks!

 

[wjm11]

Imagine that the post office only sold stamps in 5-cent and 7-cent denominations. What amounts of postage could you buy, and what amounts could you not buy?

you can buy 5,7,10,12,14,15,17,19,20,21,22 cents worth of stamps and then anything 24 cents and higher. The only ones you can't buy are 1-4, 6,8,9,11,13,16,18,23 cent stamps. Is this correct?

This is correct.

Your smallest denomination is 5 cents, so you need to find the first set of 5 consecutive number solutions (24, 25, 26, 27, 28) that can be made with 5 and 7 cent stamps. After that, it is obvious that you can add 5 to each of these to generate the next 5 numbers, and so on. There will be no more gaps in coverage. Make sense?

 

[baileygirl76]

Imagine that the post office only sold stamps in 5-cent and 7-cent denominations. What amounts of postage could you buy, and what amounts could you not buy?

you can buy 5,7,10,12,14,15,17,19,20,21,22 cents worth of stamps and then anything 24 cents and higher. The only ones you can't buy are 1-4, 6,8,9,11,13,16,18,23 cent stamps. Is this correct?

This is correct.

Your smallest denomination is 5 cents, so you need to find the first set of 5 consecutive number solutions (24, 25, 26, 27, 28) that can be made with 5 and 7 cent stamps. After that, it is obvious that you can add 5 to each of these to generate the next 5 numbers, and so on. There will be no more gaps in coverage. Make sense?

Yes. Thank you very much!!