January 27, 2014 9:23 PM Subscribe

I'm trying to help my 3rd grader with his math homework, but we are stuck on one problem. I can solve it using Algebra, but I'm trying to figure out how to explain it to him using the Singapore method that he's taught in school. Note that he hasn't learned how to add negative numbers, which puts a crimp on the methodology.

Problem: In 2 years, Tom will be twice as old as he was 5 year ago. How old is Tom now?

My solution: x+2=2(x-5). If you solve for x, the answer is 12

The Singapore solution? This is where I am stuck. I don't understand how to use the bar ("strip diagram") method to model the problem in a way that a 3rd grader taught the Singapore method can solve.

Problem: In 2 years, Tom will be twice as old as he was 5 year ago. How old is Tom now?

My solution: x+2=2(x-5). If you solve for x, the answer is 12

The Singapore solution? This is where I am stuck. I don't understand how to use the bar ("strip diagram") method to model the problem in a way that a 3rd grader taught the Singapore method can solve.

[_____?_____][___5___][___2___]

[____________________________]

I think.

posted by SLC Mom at 9:38 PM on January 27

[____________________________]

I think.

posted by SLC Mom at 9:38 PM on January 27

I agree with the previous posts. I think to explain this most clearly, you should divide it into two problems.

1) What is the future age? 2+5+(2+5)=14

2) What is the current age? 14-2=12

posted by tinymegalo at 9:41 PM on January 27

1) What is the future age? 2+5+(2+5)=14

2) What is the current age? 14-2=12

posted by tinymegalo at 9:41 PM on January 27

Parent in Singapore. No algebra until grade 6 or 7 here. I think it would go like this:

|-----------------|------5------|--2--|

\_____1/2_____/\_____1/2______/

Where you would draw curly brackets underneath to show that each box is 1/2 and 1/2 (split into 5/2) fractionwise (equal parts) and then you could say that:

Tom in two years is: (5+2) / 1/2 = 7*2 = 14

Tom is now: 14-2 = 12

posted by viggorlijah at 11:05 PM on January 27

|-----------------|------5------|--2--|

\_____1/2_____/\_____1/2______/

Where you would draw curly brackets underneath to show that each box is 1/2 and 1/2 (split into 5/2) fractionwise (equal parts) and then you could say that:

Tom in two years is: (5+2) / 1/2 = 7*2 = 14

Tom is now: 14-2 = 12

posted by viggorlijah at 11:05 PM on January 27

I'd draw it like this. Start with a bar marked to indicate "present" (using an I below):

I

Add two dashes ("In two years...")

I--|

_2_

Here's where it gets kind of tricky. I had to jump ahead to the end ("... as he was 5 years ago."):

|-----I--|

__5___2_

Then go back to the middle of the sentence and add the last segment, noting that time increases to the right:

|-------|-----I--|

\__?__/\_5_|_2_/

Neat method!

posted by disconnect at 7:39 AM on January 28

I

Add two dashes ("In two years...")

I--|

_2_

Here's where it gets kind of tricky. I had to jump ahead to the end ("... as he was 5 years ago."):

|-----I--|

__5___2_

Then go back to the middle of the sentence and add the last segment, noting that time increases to the right:

|-------|-----I--|

\__?__/\_5_|_2_/

Neat method!

posted by disconnect at 7:39 AM on January 28

Thanks, everyone! Every answer on here looks correct. I marked a couple as the best answer because they explained a couple of extra steps that are important from a 3rd graders perspective, but I was really impressed with all of the responses.

Thanks for the help!

posted by agog at 9:48 PM on January 29

Thanks for the help!

posted by agog at 9:48 PM on January 29

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|--------------|---------|----|

\_____?____/\__5___/\_2_/

? = 5 + 2

posted by one_bean at 9:35 PM on January 27 [1 favorite]