Bar Model Homework Question

[Huggie Bear]

I knew I would get stumped by my kid's math some day, but it happened way sooner that I expected. Here is the question:

Solve. Show your work. Draw bar models to help you.

Alex had 200 more magnets that Kevin did at first. After Alex gave away 340 magnets and Kevin bought another 120 magnets, Kevin had 3 times as many magnets as Alex. How many magnets did Alex and Kevin have altogether at first?

 

[Steven G]

Is that really meant to be done without algebra? You did post it in pre algebra section

 

[Huggie Bear]

It's 3rd grade math that's supposed to be solved using bar models. I guess maybe they're doing baby-steps algebra without knowing it?

 

[lev888]

This is the first time I'm using this method.
Draw the end result: 1 block for Alex and 3 blocks (of the same size) for Kevin. The difference between them is 2 blocks. What's included in the difference? What Alex lost (taking into account 200 extra he had in the beginning) and what Kevin gained. Alex lost 340 - 200 = 140. Kevin gained 120. So the 2 extra blocks Kevin has at the end consists of 140 + 120 = 260 magnets. One block is 130. So in the end Alex had 130 and Kevin 130*3 = 390. Going backwards, Alex started with 130 + 340 = 470, Kevin started with 390 - 120 = 270. Total: 470 + 270 = 740.