A bit of lockdown home schooling got us stumped...

[MysteryLemon]

We are currently going through decimals with my 9 year old daughter. Shes learning subtracting decimals today and doing a great job with the sums but this puzzle has us all a bit confused.

I can't seem to work out how we can find the length of each piece without knowing the length of at least one of the pieces of wood. We know the overall length of all of the pieces of wood combined but I can't see how we can find the individual lengths of wood from the information given. What am I missing here?

I have access to the answers (hence the rough patch tool job on the image) but knowing the individual answers isn't helping. They make sense on their own and follow the information in the question but there is no information given about how to solve the question.

Some help please?

[DickyC]

Today you are introducing equations into the curriculum.

[blueg33]

Just use Google!

The answer is here

Google Search gives answer

[omniflow]

It looks a bit complicated for a 9 year old.

Taking the shortest piece as x you've got

x+x+20+x+43=90
x+x+x=27
x=9

[lyricalgangster]

Let x be the length of the middle piece...

then the longer piece is x + 0.2

the third is x - 0.23

and take it from there!

[MysteryLemon]

blueg33 said:

Just use Google!

The answer is here

Google Search gives answer

Yup thats the page we have and what I took a picture of.

The answers don't help as they don't explain how to actually work out the answers.

From the other replies it seems this is actually beyond what our daughter knows and is expect to know. They haven't been taught equations in her class yet. I didn't learn that sort of thing until well into secondary school. I was expecting to be missing something simple.

[Wheatsheaf]

All pieces together = 0.9m

Piece 1 = x + 0.2
Piece 2= x
Piece 3 = x - 0.23

x + (x - 0.23) + (x + 0.2) = 0.9

Add 0.23 to each side
x + x + x + 0.2 = 1.13

Subtract 0.2 from each side
x + x + x = 0.93

3x = 0.93

x = 0.31m

Substituting x above gives....
0.31 + 0.51 + 0.08 = 0.9

Proved Does seem a bit hard for a 9-year old though... I'll try it on my son later.

[MysteryLemon]

omniflow said:

It looks a bit complicated for a 9 year old.

Taking the shortest piece as x you've got

x+x+20+x+43=90
x+x+x=27
x=9

Indeed. I didn't do stuff like that until well into secondary school. Not sure why this question is on a worksheet for kids in Year 5. They haven't touched on anything like that and whoever wrote the paper shouldn't have just assumed kids starting to learn decimals would just know and understand equations.

[SCEtoAUX]

You need to subtract 2B from 0.9m where B is the width of the saw blade.

[MysteryLemon]

Wheatsheaf said:

All pieces together = 0.9m

Piece 1 = x + 0.2
Piece 2= x
Piece 3 = x - 0.23

x + (x - 0.23) + (x + 0.2) = 0.9

Add 0.23 to each side
x + x + x + 0.2 = 1.13

Subtract 0.2 from each side
x + x + x = 0.93

3x = 0.93

x = 0.31m

Substituting x above gives....
0.31 + 0.51 + 0.08 = 0.9

Proved Does seem a bit hard for a 9-year old though... I'll try it on my son later.

Thanks for taking the time to write all of that out. This is well beyond anything she has learn't in school so far. This is supposed to be a paper teaching the basics of subtracting simple tenths and hundredths. Throwing in a question that assumes they know and understand equations is a little advanced

[Wheatsheaf]

MysteryLemon said:

Thanks for taking the time to write all of that out. This is well beyond anything she has learn't in school so far. This is supposed to be a paper teaching the basics of subtracting simple tenths and hundredths. Throwing in a question that assumes they know and understand equations is a little advanced

No problem and I would agree... I've had a look at the rest of that paper and I'd like to think my 9-year old can cope with all of it....apart from that question. I'l find out during our home school session later on today.

[blueg33]

I agree, too advanced. I showed it to my 18 year old daughter who is doing A levels - she told me to get lost........

Showed it to 24 year old son who is an acoustic engineer, he said "haven't done anything that simple in years, ask my sister"

I am crap at maths

[g3org3y]

Where Piece 2 = X.

0.9 = X + (X+0.2) + (X-0.23)
0.9 = X + X + 0.2 + X - 0.23
0.9 = 3X - 0.03
0.93 = 3X
0.93/3 = X

X = 0.31

Piece 1 = 0.51
Piece 2 = 0.31
Piece 3 = 0.08

0.51 + 0.31 + 0.08 = 0.9

Edit: beaten to it by Wheatsheaf.

MysteryLemon said:

We are currently going through decimals with my 9 year old daughter.

Seems rather complex for 9 years old tbh!

Edited by g3org3y on Wednesday 22 April 11:34

[DickyC]

Part of the test is to see which parents are doing the homework.

[g3org3y]

DickyC said:

Part of the test is to see which parents are doing the homework.

[jfdi]

SCEtoAUX said:

You need to subtract 2B from 0.9m where B is the width of the saw blade.

[TwigtheWonderkid]

I did it by trial and error! I started at 0.5, 0.3 & 0.07 and that came to 0.87. So then it was obvious.that I just needed to add 1cm to each to make it work.

[Douglas Quaid]

Likewise. Took me a minute to find the answer without having to use an equation, just started at 30 for second piece and adjusted it from there.

[Baldchap]

SCEtoAUX said:

You need to subtract 2B from 0.9m where B is the width of the saw blade.

[GliderRider]

DickyC said:

Part of the test is to see which parents are doing the homework.

This, or to see which pupils can use Google. Plus, to see how good the parents are at equations for when the kids start doing them for real.

Give the wrong answer now, and you won't be suspected of helping them later on!