Board logo

Maths problem
Slater - 22/1/19 at 09:01 AM

Help....... I used to be good at maths, but my daughter has stumped me with this one:

x = 0.436 (with the 3 and 6 being recurring)

Prove algebraically that x can be written as 24/55


I might post some others.....working through them right now.

tegwin - 22/1/19 at 09:09 AM

24 divided by 55 equals 0.43636363 which equals x therefore x equals 24/55?

russbost - 22/1/19 at 09:48 AM

Tegwin, I don't think that counts as an "algebraic proof"

Slater - 22/1/19 at 09:49 AM

Surely it can't be as simple as that, I think there needs to be some algebra in there somehow.

What a strange question.....

liam.mccaffrey - 22/1/19 at 09:57 AM

let x=0.436 recurring
multiply both side by 10 gives
10x= 4.36 recurring

multiply both side by 1000 gives
1000x= 436.36 recurring

therefore (1000x - 10x) = 436.36r -4.36r (this gets rid of the recurring decimal)

This gives

990x = 436-4

990x = 432

rearranging gives

x = 432/990
simplifies to

x= 24/55

wylliezx9r - 22/1/19 at 10:07 AM

24/55=0.436=x

24=0.436*55=55X

24= 23.98 = 55x

23.98/24 = 55X/24

23.98/4 CANCELS DOWN TO 1 (OR WOULD OF IF I HAD A PROPER CALCULATOR WITH RECURRING FUNCTION)

LEAVING 55X/24

REARANGED X =24/55



[Edited on 22/1/19 by wylliezx9r]

Slater - 22/1/19 at 10:48 AM

Nice, you boys are cleverer than you look. I think Liams' solution is right, I would not have come up with that.

What a great forum this is. Thanks both.

rusty nuts - 22/1/19 at 11:37 AM

If you had asked this question 50 years ago I would have worked it out in my head.

What was the question?

nick205 - 22/1/19 at 11:55 AM

I have similar difficulties helping my kids with their maths homework.

I didn't find maths difficult at school, but age has bitten and my brain power isn't what it used to be.

Mr Whippy - 22/1/19 at 12:20 PM

the answer is 42

liam.mccaffrey - 22/1/19 at 01:31 PM

How old is your daughter, that problem is far too difficult for GCSE. A-level maybe.

Angel Acevedo - 22/1/19 at 03:21 PM

quote:
Originally posted by rusty nuts
If you had asked this question 50 years ago I would have worked it out in my head.

What was the question?


No wonder thereŽs "rusty" on your forum name...
50 years ago IŽd have mumbled "gu-gu-da-da"

wylliezx9r - 22/1/19 at 03:43 PM

quote:
Originally posted by Slater
Nice, you boys are cleverer than you look. I think Liams' solution is right, I would not have come up with that.

What a great forum this is. Thanks both.


I think you'll find both solutions are correct but just done in different ways. I haven't been able to show all the working with my method - it's very difficult to show the cross cancellation and re-arrangement but its very basic algebra probably A-level.

SteveWalker - 22/1/19 at 04:00 PM

quote:
Originally posted by nick205
I have similar difficulties helping my kids with their maths homework.

I didn't find maths difficult at school, but age has bitten and my brain power isn't what it used to be.


I can still do the maths they do today - once I can figure out the meaning of the question. So many terms and methods seem to have changed names.

02GF74 - 22/1/19 at 04:55 PM

quote:
Originally posted by wylliezx9r
quote:
Originally posted by Slater
Nice, you boys are cleverer than you look. I think Liams' solution is right, I would not have come up with that.

What a great forum this is. Thanks both.


I think you'll find both solutions are correct but just done in different ways. I haven't been able to show all the working with my method - it's very difficult to show the cross cancellation and re-arrangement but its very basic algebra probably A-level.


Sorry but no. , Liam subtraction gets rid of the recurring sequence, whereas yours would only work if you had a calculator that can represent decimals to an infinite number of places, which don't exist.

steve m - 22/1/19 at 07:00 PM

Im with Mr Whippy,

42

Andybarbet - 22/1/19 at 08:04 PM

42 Spot on :-)

Slater - 22/1/19 at 08:40 PM

Hi, daughter is 15, doing GCSE Maths level 1. I took Maths O level age 15 and somehow got an A, but that question stumped me.

She says a big thank you to Liam, and that Mr Whippy must be a fool.

Obviously too young for HHGTTG.

liam.mccaffrey - 22/1/19 at 09:54 PM

I knew that maths degree would come in handy........one day

nick205 - 23/1/19 at 09:27 AM

quote:
Originally posted by Angel Acevedo
quote:
Originally posted by rusty nuts
If you had asked this question 50 years ago I would have worked it out in my head.

What was the question?


No wonder thereŽs "rusty" on your forum name...
50 years ago IŽd have mumbled "gu-gu-da-da"



50 years ago I don't think I was even a thought in my parents heads (I'm the oldest of 3 children by the way)

Mr Whippy - 23/1/19 at 12:29 PM

quote:
Originally posted by Slater
Help....... I used to be good at maths, but my daughter has stumped me with this one:

x = 0.436 (with the 3 and 6 being recurring)

Prove algebraically that x can be written as 24/55


I might post some others.....working through them right now.


anyway why are you doing her home work? tell her to do it herself the cheater

I've probably forgot 99% of the maths I got at school, makes not difference tbh, I have excel here to do it for me or google if I get stuck

I'm just waiting for the micro chip they stick in your head that gives you access to the internet just by the power of thought

Then I'll be