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Maths Help thread - Q & A


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#1 Sincerely

Posted 20 February 2019 - 07:16 PM

This Maths thread is primarily intended for EB members to help each other brush up on their maths skills. Feel free to post any maths questions or answers in this thread, but please be aware of the following:

1) Members might post their workings to seek feedback from others - their answers may frequently contain errors. No responsibility is taken for errors in this thread. Students should seek help from their maths teachers/tutors as this forum isn't intended to replace formal channels of learning.

2) No member has undertaken responsibility to answer questions, therefore some posts may not be addressed for a while, or at all. You could also try specific maths forums (eg. Mathematics Stack Exchange) where maths experts are more frequently found.

When you post a question, it might be helpful to state the relevant  year/grade (if applicable) as a guide for those who might attempt a response.

Edited by Sincerely, 21 February 2019 - 09:27 PM.


#2 Tyrannosaurus

Posted 03 March 2019 - 05:45 PM

Hi, i have a few of maths questions if anyone can help?

1> After a 9% wage increase a mans's salary is $38150. What was his wage before the increase?

2> After a 20% reduction in sale prices a mountain bike was $380. How much did it cost before the reduction?

3> Jim took 40min to reach his office, drove at a speed of 54m/min. John took 24 min to reach this office , travelling the same distance as Jim. Calculate the average speed of John in m/min.

4> A calculator and two pencils were purchased at a cost of $36. If the calculator was twice the cost of the two pencils, how much was each pencil?

Edited by Tyrannosaurus, 03 March 2019 - 05:52 PM.


#3 tayto...

Posted 03 March 2019 - 06:18 PM

The new salary is 109% of the original salary. $38150 divided by 109 gives 1% of the original ($350) then times this by 100 to get 100% of the original = $35000
Sorry, hard to explain via message!

#4 tayto...

Posted 03 March 2019 - 06:20 PM

Similar principle for 2 - the sale price is 80% of the original (100-20). So 380 divided by 80 times 100 = 475

#5 tayto...

Posted 03 March 2019 - 06:24 PM

Distance Jim travelled = 40mins times 54metress each min = 40 x 54 = 2160 metres

Johns speed in metres per minute is 2160metres divided by 24 mins = 90m/min

#6 tayto...

Posted 03 March 2019 - 06:27 PM

Calculator price = 2 x pencil price
Write in algebra as c = 2p

C + 2p = $36
But as C is the same as 2p can say
2p + 2p = 36
4p =36
P=9

Pencil costs $9

Happy to explain any of the steps in any of them (and hope I’ve made no errors, hard on phone!)

#7 seemingly

Posted 03 March 2019 - 06:30 PM

#4

total = 36
calculator = c
pencils = 2p

c = 2(2p) = 4p

36 = 2c + c

36 = 2(4p) + 4p

36 = 8p + 4p

36 = 12p

36/12 = p

p = 3

Check working.

36 = 2(4x3) + 4(3)

36 = 2(12) + 12

#8 tayto...

Posted 03 March 2019 - 06:39 PM

Ahh sorry I read no4 wrong! Thought the calculator was twice the cost of ONE pencil but it’s twice the cost of 2

So

C = 2 times 2p = 4p

C + 2p = 36
But c = 4p
4p + 2p = 36
6p = 36

P = 6

Edited by tayto..., 03 March 2019 - 06:44 PM.


#9 BBC

Posted 03 March 2019 - 06:49 PM

4 with no algebra

Calculator and 2 pencils cost $36
Calculator is twice the cost of 2 pencils.

Twice the cost of the two pencils, plus the cost of the two pencils is 3 times the cost of the two pencils.

3 x 12 = 36

So the two pencils cost $12 and the calculator cost $24
So one pencil costs $6

Check: 24 + 6 + 6 = 36
24 (calculator) is double 12 (2 pencils at 6 each)

#10 PatG

Posted 03 March 2019 - 06:51 PM

View PostBBC, on 03 March 2019 - 06:49 PM, said:

4 with no algebra

Calculator and 2 pencils cost $36
Calculator is twice the cost of 2 pencils.

Twice the cost of the two pencils, plus the cost of the two pencils is 3 times the cost of the two pencils.

3 x 12 = 36

So the two pencils cost $12 and the calculator cost $24
So one pencil costs $6

Check: 24 + 6 + 6 = 36
24 (calculator) is double 12 (2 pencils at 6 each)

It's still algebra! Which is why algebra is so cool. People need to realise that algebra is just logic, it isn't some mysterious magic.

#11 seemingly

Posted 03 March 2019 - 06:51 PM

I made a mistake in mine =.=

#12 Sincerely

Posted 03 March 2019 - 08:04 PM

View Postseemingly, on 03 March 2019 - 06:51 PM, said:

I made a mistake in mine =.=

The error was in this line: 36 = 2c + c

Your algebra manipulations are impeccable. It was just incorrect interpretation/translation of the word statement to the equation.

You've probably already worked this out, but given this thread has a broader purpose, I have stated this for the benefit of others.

Edited by Sincerely, 03 March 2019 - 08:37 PM.


#13 LucyGoose

Posted 03 March 2019 - 10:07 PM

What grade was this Tyrannosaurus?

Edited by LucyGoose, 03 March 2019 - 10:08 PM.


#14 Sincerely

Posted 04 March 2019 - 07:11 PM

Many thanks to BBC for setting out the word statements for each equation step of the solution to Q4:

Calculator and 2 pencils cost $36

C + 2P = 36

Calculator is twice the cost of 2 pencils.

C = 2 x 2P

Twice the cost of the two pencils, plus the cost of the two pencils is 3 times the cost of the two pencils.

C + 2P = 36

(2 x 2P) + 2P = 36  

3 x 2P = 36

Since 3 x 12 = 36,

2P = 12    Two pencils cost $12

P = 6        So one pencil costs $6


In addition,

(2 x 2P) = 24  

C = 24   The calculator cost $24




#15 Tyrannosaurus

Posted 04 March 2019 - 10:11 PM

Thanks everyone!

#16 Sincerely

Posted 09 March 2019 - 01:40 PM

I'm glad no one is having problems with maths but I must say I'm surprised that there haven't been more users.

#17 ipsee

Posted 09 March 2019 - 04:46 PM

Homework has just started here this week so it may take off soon :)

#18 BBC

Posted 09 March 2019 - 05:05 PM

Agree my solution is really algebra, but primary school style keeping away from symbolic notation.

#19 can'tstayaway

Posted 10 March 2019 - 10:15 AM

View PostSincerely, on 09 March 2019 - 01:40 PM, said:

I'm glad no one is having problems with maths but I must say I'm surprised that there haven't been more users.
My kids are ok with maths but when they did have trouble, I would insist they leave the question unanswered and ask the teacher. It’s feedback so the teacher knows what their ability level is and doesn’t move ahead on work or give extra work at an unsuitable level. This is at schools where I know the teachers have time though. If I didn’t believe they would get an understanding or suitable explaination, I’d definitely be helping them to solve problems.

#20 Sincerely

Posted 10 March 2019 - 03:07 PM

View Postcan, on 10 March 2019 - 10:15 AM, said:


My kids are ok with maths but when they did have trouble, I would insist they leave the question unanswered and ask the teacher. It’s feedback so the teacher knows what their ability level is and doesn’t move ahead on work or give extra work at an unsuitable level. This is at schools where I know the teachers have time though. If I didn’t believe they would get an understanding or suitable explaination, I’d definitely be helping them to solve problems.

It's great that you're confident to help your kids with maths. I started this thread because on multiple threads, several members had expressed a wish to be better at maths, so whilst I had expected that most posts would be to get help with homework, I thought this might give some the opportunity to brush up on dusty high school maths skills (I got real satisfaction the other day from helping DS work out how to graph a function from the graph of its first derivative - haven't come across that in over thirty years as the only maths I get to do in my profession is a little bit of population statistics).

#21 JayPee

Posted 20 March 2019 - 02:10 AM

Came across this article on news.com.au about a quiz which has stumped the internet, cue eyeroll.

One of the questions was as follows:

12 ÷ 2 (5-2)

I applied bimdas (or so I thought) and got 2 as my answer. But the correct answer is 18. Why?

My working:
12 ÷ (2 × (5-2))

And I guess theirs is:
(12÷2)(5-2)

Here is the link for those interested:

https://www.news.com...9662348b677ee58

#22 PsySquirrel

Posted 20 March 2019 - 03:33 AM

Is it because after you do the brackets everything else is in the order of the equation?

12/2x(5-2)

12/2x3
6x3
18


Ideally they would make the equation look like this:

12
2    x (5-2) = 18

Otherwise it looks like this to me:

     12    
2x(5-2)      = 2

#23 qak

Posted 20 March 2019 - 04:30 AM

There was a similar one a few months ago.
*I* disagreed with their answer, but it turns out that what I learnt is out of date ... it is to do with the 2(5-2).

The rule now (as applied to the equation in question) is that you do the brackets first (as normal) but then its strictly left to right.

Whereas I *think* I was taught the 2(5-2) would take priority to be calculated?

#24 Sincerely

Posted 20 March 2019 - 07:21 AM

In a school textbook teaching order of operations, one would expect to see all the operation signs: 12 ÷ 2 x (5-2), but where equations are used as part of a profession, the format on the Internet, 12 ÷ 2 (5-2), is correct and concise, efficient use of type characters.

#25 seayork2002

Posted 20 March 2019 - 08:09 AM

12/2(5-2)

I work it out as

12/2x3                              (as 5-2=3)

12/2=6x3 = 18

so I get 18?




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