At the risk of wearing a dunce cap - I have a math question....

[dorothy]

In the Singapore 4A textbook they have the following problem:

Sean has 1135 stamps. He has 3 times as many foreign stamps as U.S. stamps. How many stamps does he have altogether.

They go on to work out the problem as 1135 x 4 = 4540 total stamps.

OK - here's the thing, I would have done the problem as 1135 x 3 = 3405.

Why is it x4 if it is 3 times as many?

I feel like a total dork asking this. Please be gentle. Thanks.

[LisaNY]

Hi Dorothy,

If you do a bar diagram, it's easier to see why:

|---| (this represents his 1135 US stamps)
|---|---|---| (this represents his foreign stamps)

If they are looking for a *total* # of stamps, you can see how
they have to multiply by 4, and not 3.

You could figure it out the way you were thinking by multiplying
1135 by 3, and then adding the other 1135 for the grand total of stamps.

Does that make sense? I think I've figured this correctly, but others can chime in if I bombed this. :rolleyes:

[St. Theophan Academy]

not my area - should not be posting here, but here goes-

first, I am assuming the first part of the problem actually said Sean has 1135 "US" stamps. He has 3 times as many foreign stamps as U.S. stamps. How many stamps does he have altogether.

If you multiply by 3 you will get the number of foreign stamps, but that will not give you the number of TOTAL stamps, you would have to then add the number of US stamps - so 3 x 1135 = number of foreign stamps, then add the original US stamps (1135) to get a total. So they are just showing you that you can eliminate a step and multiply by 4 to get the total number of stamps. Does that make sense?

Anne Marie

[chai]

Sean has two sets of stamps one US and one foreign. The problem states that he has 3 times as many foreign stamps as US stamps. If you multiply the US stamps by 3, you will get the total number of foreign stamps. But, in order to get the total, you need to add the foreign stamps and the US stamps together. This has the same affect as multiplying the US stamps by four.

Did that make sense? It is helpful to draw a bar chart. Then you can see why this is the answer.

[chai]

After I posted my reply, I saw that others beat me to answer. At least we all said the same thing! :D

[dorothy]

that I didn't pay attention to the end. I kept wondering why it was x4 - duh!

I would have taken the extra step and done x3 then + 1 more because I am not math efficient.

Thanks everyone!!!!