Maths Help thread  Q & A
Started by
Sincerely
, Feb 20 2019 07:16 PM
81 replies to this topic
#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 (10020). 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.
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)
Posted 03 March 2019  06:51 PM
BBC, 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
seemingly, 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.
Posted 09 March 2019  04:46 PM
Homework has just started here this week so it may take off soon
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
Sincerely, 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
can, 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 (52)
I applied bimdas (or so I thought) and got 2 as my answer. But the correct answer is 18. Why?
My working:
12 ÷ (2 × (52))
And I guess theirs is:
(12÷2)(52)
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(52)
12/2x3
6x3
18
Ideally they would make the equation look like this:
12
2 x (52) = 18
Otherwise it looks like this to me:
12
2x(52) = 2
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(52).
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(52) 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 (52), but where equations are used as part of a profession, the format on the Internet, 12 ÷ 2 (52), is correct and concise, efficient use of type characters.
#25
seayork2002
Posted 20 March 2019  08:09 AM
12/2(52)
I work it out as
12/2x3 (as 52=3)
12/2=6x3 = 18
so I get 18?
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