Maths Help

Please can you answer these questions and show me how to work them out?

1.Rearrange y=ax+c to make x the subject

2.Solve the simultaneous equations
2x-3y=11
5x+2y=18

3. A straight line has equation y=2(3-4x) find the gradient of the straight line

4. Solve 20y-16=18y-9

5. A year ago donna weighed 51.5g donna now weight 8.5% less. Work out how much donna now weighs give your anwser to a apporiate degree of accuracy

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Reply 1

dezlee

1. Rearrange to do what?
2. Cannot be bothered
3. -8
4. cannot be botehred
5. 47.1g

Reply 2

arpeggio

1. ? Question doesn't say which letter to make the subject (if that's even what it's asking)
2. OK. Right. You have the two equations:
1) 2x - 3y = 11
2) 5x + 2y = 18
You need to make either the 'x's or the 'y's the same in order to cancel them out. I multiplied the first one by 2 and the second one by 3 so that the 'y's are both the same. But you have to remember to multiply everything in the equation by the number. So I got:
1) 4x - 6y = 22
2) 15x + 6y = 54
Now to cancel out the 'y's I'm going to have to add the equations together, because -6y + 6y = 0. This leaves me with:
19x = 76 (then divide by 19)
x = 76/19
x = 4
Taking th x as 4, go back to one of the original equations and substitute it in.
e.g. (2x4) - 3y = 11
8 - 3y = 11
8 = 11 + 3y
3y = 8 - 11
3y = -3
y = -1

You can check your answers by substituting the numbers into the other original equation like so:
(5x4) + (2x-1) = 18
20 + -2 = 18
20 - 2 = 18
Therefore the working is correct and x = 4 and y = -1.

Tell me if you understand this and if not I'll try and explain more. It's really very simple once you get the hang of it.

For the other questions I got:
3. 8
4. y = 3.5
5. 47.1kg (to 1 d.p.)

I'm happy to explain these as well if you want - just let me know! And to dezlee: are you sure about number 3? I'm pretty sure it's 8, not -8.

Reply 3

arpeggio

Whoa sorry about that, it was more long-winded than I realised :p:

Reply 4

Master621

2. x=4 and y=-1
4. y=3.5

Nothing like year 7 maths to build up an appetite :smile:

Nevermind she got there first.

Reply 5

Swayum

xemmajanex

dezlee: are you sure about number 3? I'm pretty sure it's 8, not -8.

It is -8.

y=2(3-4x)
y = 6 - 8x

Using the equation, y = mx + c (where m is the gradient and c is the y intercept), it's clear that the gradient is -8.

Reply 6

arpeggio

Yes, but I thought you had to rearrange it in the format y = mx + c - I might be trying to overcomplicate it, but once you rearrange it in that format you get y = 8x + 6, which is where I got the 8 from.

Reply 7

Naranoc

Nope, it is -8.

Look, y=2(3-4x) multiplies out to give y=6-8x right?

Well, y=6-8x is EXACTLY the same as y= -8x + 6. It's like saying 5+2 is the same as 2+5. The signs ONLY get swapped over if they pass through an equals sign:

e.g.

-8x + 2 = 10x would become 2 = 10x + 8x if you moved the 8x over.

Reply 8

MulletMan

Would i about the questions in the attachments, the reason i did not write them out is cause you either need the picture of the data.

Reply 9

MulletMan

Also how did you work out 3, 4 and 5?

Reply 10

Yuanfen

The banknotes question in the images is testing knowledge of similar figures. If two shapes have the same ratio of sides, and one is just an enlargement of the other, then they are mathematically similar.

So if we say the first banknote has height H1 and length L1, and the second banknote has height H2 and length L2,

For the banknotes to be similar, then

H1/L1 = H2/L2

Edit: tried making it look like a real equation but didn't work

Reply 11

MulletMan

Can anyone help with these???

Reply 12

MulletMan

Please I really need help with these i have test on monday any help will be very much appreciated

Reply 13

Berto90

MulletMan

Please I really need help with these i have test on monday any help will be very much appreciated

which one exectly? i loko up and i see replys, are these unclear or something?

Reply 14

calcium878

1. x = (y-c)/a

i think the rest have been answered

Reply 15

MulletMan

What about the attachments they have questions, can someone help with them please

Reply 16

Cataclysm

All of your attachments have been answered above, look at xemmjanex's post

Reply 17

tiger_vio

it's definitely -8. If you bring the 6 past the -8, you aren't taking anything over an equals sign or anything- it stays as -8!

Reply 18

MulletMan

The attached images haven`t been answered.

Reply 19

Eternity Forever

MulletMan

What about the attachments they have questions, can someone help with them please

ok for the first one, some one has already answered it for you. If they were similar they would have to be in a similar ratio to each other, for example 1:2 is similar to 2:4.

Second attachment:
I cant see the question, but I am guessing it is asking for the volume? If so, then to find the volume of a cylinder you use the simple formula; pie*radius^2*height.
Therefore; pie*9.3^2*12.4
= 3369.28273
= 3369.28 to 2d.p

Third attachement:
Lets take for example if before the sales the original price waas £100.
So, 20% off £100, will leave you with £80, with £20 off

And in the next sale, 30% was taken off the sale price (£80).
Therefore 30% of £80, is £24.

So overall, 24+20 =44. Therefore, there was a 44% decrease off the original price and only 56% was left.

Fourth attachment:
For 3 month moving average, you simply need to add the first three, find the average, then next set of three, find the average and soo on until you have the last set of 3 numbers.

so, this would be: (147+161+238)/3 = 182
(161+238+135)/3 = 178
(238+135+167)/3 = 180
(135+167+250)/3 = 184

fifth attachment:

ok, so first of all when estimating the mean off this kind of table, you will have to know that;
Mean = sum of fx/sum of f.
f=frequency
x=midpoint.

Now you had to find the midpoint for each interval and will always have to do this before doing the estimate mean.

You find the mid point, multiply it by the frequency in the same interval to get "fx"
so, first interval =(2+0)/2 = 1, which is the midpoint.
so fx=
first interval - 1*10=10
second interval-3*15=45
third interval-5 *30=150
fourth interval-7*35=245
fifth interval-9*25=225
sixth interval-11.*5=55

Therefore if you find the sum of fx, it will be 730.
Now remember there are 120 children, so this is the sum of f

So to find the mean you now do, 730/120 = 6.08333333.....
The question asked for the mean correct to 2d.p

so, the estimate mean is 6.08 hours.

Hope that helps.