Hi, how do I solve this problem with modelling? Thanks

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primary 5 Maths Fractions Singapore

Hi, how do I solve this problem with modelling? Thanks

Date Posted: 5 years ago

Comments 6 add a comment

Chow Sihui

5 years ago

Do i have to draw models?

Sim

5 years ago

No need to

Chow Sihui

5 years ago

Is it okay to use algebra to explain?

Sim

5 years ago

Yes

Phylicia Tong

5 years ago

Hi, you might wan to make the number of 5kg and 2kg bags the SAME
ie add 4 more 2kg bags or take away 4 5kg bags.

Let's say i add 4 more 2kg bags (ie 'make the 2kg number of bags = 5kg bags"..... Therefore 4x2 = 8kg will be added. Total weight will then be 272 + 8 = 280kg.

Now, no. of 5kg bags = no. of 2kg bags, the weight of 1 group of bags = 5+2 = 7kg.

1 group of 7kg = 280
No. of groups = 280/7 = 40.

Total 80 bags but i added 4 bags to the 2kg, so actual = 80-4 = 76.

Can understand?

Sim

5 years ago

Thanks for clarifications

See 2 Answers

done {{ upvoteCount }} Upvotes

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Let me know if you do not understand my modelling or my workings.

Date Posted: 5 years ago

Comments 7 add a comment

Sim

5 years ago

Why is 4 = 20kg? How you arrive at 20?
Thanks

Eric Nicholas K

5 years ago

Each of the 4 bags has a mass of 5 kg, so the total is 20 kg.

First model is for the number of bags, second model is for the masses.

By doing up the model for the masses, we can include the number 272.

There are an unknown mass of ‘7-kg’ bags (each 7-kg bag is equal to one 5-kg bag PLUS one 2-kg bag). With the extra 20 kg coming from the 4 extra bags, the total mass is 272 kg. It follows that the total mass of the ‘7-kg’ bags is 252 kg.

There must have been 36 of such '7-kg' bags to get 252 kg. This means that there are 36 of 5-kg bags and 36 of 2-kg bags.

Remember that there are 4 more 5-kg bags.

So the total is 36 + 36 + 4 = 76 bags.

Sim

5 years ago

Can we use 36 of 7 kg since 2+5kg = 7kg. Which makes it 36 + 4 = 40 bags altogether?

Eric Nicholas K

5 years ago

Basically what I did was to combine one 5 kg bag with one 2 kg bag into a single large 7 kg bag.

So one large 7 kg bag is actually made up of TWO bags, one each of 5 kg and 2 kg.

You can check at the end that 40 bags of 5 kg each and 36 bags of 2 kg each gets you 272 kg altogether.

Eric Nicholas K

5 years ago

When I did my calculations, I obtained 36 large 7 kg bags. This is made up of 36 small 5 kg bags and 36 small 2 kg bags.

Chow Sihui

5 years ago

There is a total of 36 sets of 7kg bags. And one 7kg bag is made out of one 5kg and one 2kg bag.

So 36 sets of 7kg bags means that there are 36 bags of 5kg AND 36 bags of 2kg.

So the number of bags is 36(7kg bags) and 36(2kg bags). But we cannot forget the extra 4 bags of 5kg.

So its 36+36+4=76.