# Talk

Threads in this topic are removed 90 days after the thread was started.

## Maths Help

(24 Posts)
Lindyroo Tue 12-Dec-17 21:38:42

Hello my son needs help with these question can anyone help us please

FrostyThirties0 Tue 12-Dec-17 21:39:52

Might need bit more of a clue...

Tue 12-Dec-17 21:40:56

Would love to try!

Lindyroo Tue 12-Dec-17 21:42:26

yes sorry FrostyThirties0
Do you know how i can import a picture onto here so i can show you?

Tue 12-Dec-17 21:44:15

Use the paperclip to attach a photo

Passthecake30 Tue 12-Dec-17 21:45:28

Ooo a maths thread! Patiently waiting...

Lindyroo Tue 12-Dec-17 21:48:14

It saids a factory makes ice cream in two sizes. Small and large
The tubs are similar in shape
The height of the small tub is 5cm
The volume of the small tub is 150cm^3
The volume of the large tub is 500cm^3

Work out the heigh of the large tub
(I believe the topic is frustums)
Many thanks

Jessiegirl Tue 12-Dec-17 22:01:24

Similar shapes so lengths are in the ratio L1 : L2
Areas in the ratio (L1)^2 : (L2)^2
Volumes in the ratio (L1)^3 : (L2)^3

He’s been given both sides of the volume ratio so he now needs to work backwards.

Volume ratio is 150 : 500
Which is 3 : 10
Or 1 : 10/3

Cube root both sides 1 : 1.4938. (5 sf)
This gives new length ratio

Then times both sides by 5
5 : 7.469

So length required is 7.469
7.47 to 3 sf

(I hope this is right)

SpeverendRooner Tue 12-Dec-17 22:02:59

If the shapes are similar, each of the dimensions (length, width, height) of the larger tub will be the same multiple of the dimension of the smaller tub. So if the larger tub is twice the width of the smaller, it is also twice the height and twice the length.

Given the volume ratio, that should be enough to figure out the ratio of the sides.

Lindyroo Tue 12-Dec-17 22:03:44

This looks great thanks Jessiegirl

Lindyroo Tue 12-Dec-17 22:09:46

I do have another few if you don't mind:
1) Anna and Bil share some money in the ratio 2:5
Anna gets £A
Bill gets £B
Carl and Donna share twice as much money as Anna and Bill share.
They share money in the ratio 3:1
Carl gets £C
Donna gets £D
Find A:B:C:D
Thanks

Lindyroo Tue 12-Dec-17 22:13:31

Also
2) A solid cuboid has a volume of 40cm^3
The cuboid has a total surface area of 100cm^3
One edge of the cuboid has length 2cm

Find the length of a diagonal of the cuboid
Thanks

PurpleDaisies Tue 12-Dec-17 22:14:19

Let amount of money be x.

A gets 2/7 x
B gets 5/7 x
C gets 6/4 x
D gets 2/4 x

So ratio is 2/7:5/7:6/4:2/4 since the x cancels

Then it’s a just case of simplifying the fractions.

jingleberries Tue 12-Dec-17 22:14:47

What level maths is this??? It's not easy!!!!

multivac Tue 12-Dec-17 22:16:33

The correct answer for this homework is, "I couldn't work out how to do it. Please could you explain the principles again?"

HTH

PurpleDaisies Tue 12-Dec-17 22:17:29

To simplify multiply the sevenths by four and the quarters by seven to give a common denominator so I think the final answer is ...
8:20:42:14 which simplifies yo
4:10:21:7

Lindyroo Tue 12-Dec-17 22:30:00

Thanks all,
this is a year 9"s homework (14 year old)

Jessiegirl Tue 12-Dec-17 22:33:39

Is there a diagram for the cuboid?
Does it ask for diagonal or space diagonal?

This is very difficult work.

multivac Tue 12-Dec-17 22:36:24

I reiterate my answer. Mumsnet doing the homework on the OP's kid's behalf really isn't going to help (assuming we think that understanding maths actually matters).

Lindyroo Tue 12-Dec-17 22:38:48

Don't worry about the last question, thanks any way. i will have a word with my sons teacher.

Jessiegirl Tue 12-Dec-17 22:40:14

Well it’s not as if we’re giving the answer only. These are worked solutions.
I’d say the teacher will have to go through these questions anyway. So at least he has a bit of prior knowledge.

jingleberries Tue 12-Dec-17 22:48:49

Well I'm useless and I used to think I was quite good at maths but I have enjoyed seeing how they weee worked out so thank you for the homework all round!

AnnieanoniMouse Tue 12-Dec-17 23:05:01

Multivac

If people give their workings the OP might be able to understand how to do it & help her son learn how to do it. If he still doesn’t get it he can tell his teacher, if he doesn’t, it will soon be obvious he doesn’t understand through his classwork.

AnnieAnoniMouse Tue 12-Dec-17 23:07:30

Lindyroo. Don’t be put off asking, we all love a bit of maths homework 🤓 and the opportunity to help someone understand a little more😊

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