Maths question

[essayer]

The missus is (re)sitting her Maths GCSE and did a class last night. They are on powers/indices. She was confused by a question and my answer was different to the teacher's. The teacher said their answer was correct.



I said: Just multiply 7 and 4 so the answer is 3^28 (3^7 x 3^7 x 3^7 x 3^7)

The maths teacher said: You have to raise 3^4 as well i.e. 3x3x3x3, as well as multiplying the indices, so their answer was 81^28

I'm definitely correct aren't I?

[BlackTails]

You are correct.

The maths teacher is a fking imbecile. I’d be asking for a different teacher.

[MesoForm]

Wolfram Alpha is a handy tool for checking things like this
https://www.wolframalpha.com/input?i2d=true&i=...
https://www.wolframalpha.com/input?i2d=true&i=...
(yes, you are correct)

[cheesejunkie]

I refuse to do maths these days. My best days are behind me.

Notation should not be open to interpretation. There's a reason maths is concise.

Maths GCSEs have became a bit more advanced than when I sat one by the sounds of it though.

[CanAm]

It's over 60 years since I did my Maths O Level, but if you work it out arithmetically instead of simplifying you get the same answer as via the simplified version of 3>28, so I think you're right.
< sits back and waits to be flamed by modern mathematicians>

[Defcon5]

I’m struggling with my son’s Y6 long division, so I have no chance when he gets to GCSEs.

The above may as well be in Chinese

[otolith]

This is basic stuff, I'm shocked that the teacher gave the wrong answer. You can work the index rules out from first principles, just write it out as you did.

[Panamax]

I am absolutely not a mathematician.

My recollection is "deal with what's inside the bracket first" so it looks to me as though the teacher's right.

[Mammasaid]

Panamax said:

I am absolutely not a mathematician.

My recollection is "deal with what's inside the bracket first" so it looks to me as though the teacher's right.

Now expand the brackets correctly and count up the 3s

(3x3x3x3x3x3x3) x (3x3x3x3x3x3x3) x (3x3x3x3x3x3x3) x (3x3x3x3x3x3x3)

How many do you get?

[ApOrbital]

My head hurts.

RIP.

[Panamax]

Like I said, I'm not a mathematician. However, I was taught many years ago to solve the bracket first. On this basis I felt the "4" should be applied to the answer to the bracket - not just apply a bunch more "3"s.

Anyway, I'm happy to guided by experts! Just don't let me near the controls....

[speedking31]

Sometimes helps to consider a simpler example that can be done by mental arithmetic (3²)³ = 9³ = 729, or 3^(2x3) = 3^6 = 729, i.e. you multiply the indices.

Edited by speedking31 on Thursday 17th October 17:10

Edited by speedking31 on Thursday 17th October 17:10

[cuprabob]

Panamax said:

Like I said, I'm not a mathematician. However, I was taught many years ago to solve the bracket first. On this basis I felt the "4" should be applied to the answer to the bracket - not just apply a bunch more "3"s.

Anyway, I'm happy to guided by experts! Just don't let me near the controls....

Dealing with the bit in brackets first and that result to the power 4 is the same answer as 3 to the power 28.

[Gary C]

essayer said:

I'm definitely correct aren't I?

Yes you are.

[snuffy]

essayer said:

I'm definitely correct aren't I?

Yes,

3 to the power 7, all raised to the power 4, i.e. 3 to the power 28.

If you want to check it numerically, type it into Excel:

A1 = 3^7
B1 = A1^4

And B2 = 3^28

You will see B1 and B2 show the same result.

[Panamax]

cuprabob said:

Dealing with the bit in brackets first and that result to the power 4 is the same answer as 3 to the power 28.

Thanks, it was too big for my calculator!

[otolith]

Panamax said:

Like I said, I'm not a mathematician. However, I was taught many years ago to solve the bracket first. On this basis I felt the "4" should be applied to the answer to the bracket - not just apply a bunch more "3"s.

Anyway, I'm happy to guided by experts! Just don't let me near the controls....

The brackets are superfluous really, they're just there for clarity so you don't think it's 3^74

The power laws are very simple, and if you forget them you can work them out again from scratch.

Also, as the example is fully numeric, you can check it with a calculator and see that the teacher is wrong.

[cheesejunkie]

Agreed and understand why the question is about simplifying a problem. But there’s no way that question would have been on my GCSE paper.

Maybe if it was it would have been a good thing. GCSEs were piss easy pass in my day.

I can do laplace transforms and dfts in my head but irrelevant other than to say can do maths and looked at that question thinking why is it a question rather than what’s the answer.

[otolith]

cheesejunkie said:

Agreed and understand why the question is about simplifying a problem. But there’s no way that question would have been on my GCSE paper.

Child has just started her GCSEs this term, and I remember helping her with this at the beginning of the year, so pre-GCSE.

[Jim1064]

Stupid teacher.

You could of course simplify a bit more:
3^28 = 9^14 = 81^7 = 22,876,792,454,961

It becomes more interesting if you leave the brackets out, in that case you raise 3 to the power of (4 to the power of 7):
3^16384 = a number with 7818 digits
(if you really want to know: approximately 1.4277012078932958292545728220963e+7817)

Edited by Jim1064 on Thursday 17th October 18:49

Edited by Jim1064 on Thursday 17th October 20:17

Edited by Jim1064 on Thursday 17th October 20:17