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rogerwaters
2013-11-05 03:57:07

What is the answer to number 5?
D or A? Or something else?

bob bundy
2013-09-24 16:53:29

hi demha,

Well done for that result!

Bob

bobbym
2013-09-24 06:21:31

Hi;

Very good result.

demha
2013-09-24 03:44:27

Hi Bobbym,
I actually just wanted help to do the equation my self, not have someone else do it for me but thank you very much!

And Bob I thank you too for your help!

Sent in the lesson and got 20/20.

bob bundy
2013-09-24 03:13:49

I have a rectangle, with a length of 7 and a width of 4:

15. What is the perimeter? - Answer: E
A 31
B 26
C 58
D 35
E 22
F 59

Correct.

16. What is the area? - Answer: A
A 28
B 65
C 79
D 13
E 10
F 19

Correct.

This rectangle just became the base of a regular prism, with a height of 6:

17. What is the lateral area? - Answer: F
A 119
B 873
C 256
D 349
E 332
F 132

Correct.

18. What is the total surface area? - Answer: D
A 119
B 873
C 256
D 188
E 332
F 132

Correct.

19. What is the volume? - Answer: E
A 651
B 327
C 395
D 221
E 168
F 342

Correct.

20. What is the area of the largest rectangular side? - Answer: D
A 65
B 32
C 36
D 42
E 16
F 34

Correct.

Well done.

Bob

bob bundy
2013-09-24 03:05:16

hi demha

Firstly Q6-10 are all correct.  Well done!

Q11 and Q12 and Q14 are also correct.

I'll look at the last section in a new post

Bob

bobbym
2013-09-24 01:39:35

Hi;

For 13) you indicate that you need some help.

You have:

h = 4
b = 6
l  = 8

V = ( 4 x 6 x 8 ) / 2 = 96

demha
2013-09-24 01:31:11

I have a rectangle, with a length of 7 and a width of 4:

15. What is the perimeter? - Answer: E
A 31
B 26
C 58
D 35
E 22
F 59

16. What is the area? - Answer: A
A 28
B 65
C 79
D 13
E 10
F 19

This rectangle just became the base of a regular prism, with a height of 6:

17. What is the lateral area? - Answer: F
A 119
B 873
C 256
D 349
E 332
F 132

18. What is the total surface area? - Answer: D
A 119
B 873
C 256
D 188
E 332
F 132

19. What is the volume? - Answer: E
A 651
B 327
C 395
D 221
E 168
F 342

20. What is the area of the largest rectangular side? - Answer: D
A 65
B 32
C 36
D 42
E 16
F 34

demha
2013-09-24 01:25:11

Last 10 to go!

I have an isosceles triangle with a height of 4 and a base of 6:

11. What is the area?  - Answer: C
A 19
B 35
C 12
D 16
E 22
F 54

This triangle just became the base of a regular prism, with a height of 8:

12. What is the lateral area? - Answer: D

A 105
B 28
C 35
D 128
E 56
F 12

13. What is the volume? **need help solving
A 95
B 54
C 32
D 23
E 96
F 10

14. What is the area of the largest rectangular side? - Answer: D
A 95
B 54
C 32
D 48
E 96
F 10

demha
2013-09-24 01:13:44

The shape is a pyramid with:

6. a rectangular base with a width of 4
A Lateral area: 120; Volume: 98
B Lateral area: 192; Volume: 76
C Lateral area: 240; Volume: 51
D Lateral area: 176; Volume: 33
E Lateral area: 288; Volume: 75
F Lateral area: 100; Volume: 64

Volume:
a = 6 x 4
a = 24

v = 1/3 x 24 x 8
v = 64

Lateral Area:
6 + 4 + 6 + 4 = 20
20 x .50 = 10
10 x 10 = 100

7. a square base
A Lateral area: 120; Volume: 96
B Lateral area: 90; Volume: 64
C Lateral area: 176; Volume: 144
D Lateral area: 192; Volume: 35
E Lateral area: 288; Volume: 288
F Lateral area: 240; Volume: 75

Volume:
a = 6 x 6
a = 36

v = 1/3 x 36 x 8
v = 96

Lateral Area:
6 + 6 + 6 + 6 = 24
24 x .50 = 12
12 x 10 = 120

8. a rectangular base with a width of 3
A Lateral area: 192; Volume: 144
B Lateral area: 90; Volume: 48
C Lateral area: 276; Volume: 64
D Lateral area: 176; Volume: 144
E Lateral area: 92; Volume: 96
F Lateral area: 62; Volume: 24

Volume:
a = 6 x 3
a = 18

v = 1/3 x 18 x 8
v = 48

Lateral Area:
3 + 6 + 3 + 6 = 18
18 x .50 = 9
9 x 10 = 90

9. a rectangular base with a width of 5

A Lateral area: 100; Volume: 48
B Lateral area: 240; Volume: 112
C Lateral area: 176; Volume: 96
D Lateral area: 110; Volume: 80
E Lateral area: 288; Volume: 144
F Lateral area: 90; Volume: 64

Volume:
a = 5 x 6
a = 30

v = 1/3 x 30 x 8
v = 80

Lateral Area:
6 + 5 + 6 + 5 = 22
22 x .50 = 11
11 x 10 = 110

10. a rectangular base with a width of 7
A Lateral area: 240; Volume: 64
B Lateral area: 188; Volume: 96
C Lateral area: 176; Volume: 144
D Lateral area: 130; Volume: 112
E Lateral area: 144; Volume: 215
F Lateral area: 100; Volume: 128

Volume:
a = 6 x 7
a = 42

v = 1/3 x 42 x 8
v = 112

Lateral Area:
7 + 6 + 7 + 6 = 26
26 x .50 = 13
13 x 10 = 130

bob bundy
2013-09-23 18:27:30

hi demha,

Glad you enjoyed our discussion about these problems.  We have identified a big error with the work that Compu High are teaching you.  The teaching page is available as a 'demo' so I have been able to read it all.  The  volume calculations are fully correct but the slant height section is WRONG.

Because I am a teacher of maths, I cannot just let you do these questions without showing you the correction.  I'll do that first.  Then you'll want to get their answers so you get full marks.  That's OK.  I have used their method and Q6 to Q10 all have a 'correct' answer.  So hopefully, at the end, you will understand the work properly and be able to get full marks.    I would just add, this is not the only criticism I have of this on-line course but I won't burden you with all my objections.  Let's get on.

Correction:  If you buy some wire so you can make a wire-frame version of these pyramids, you could proceed as follows.  (see diagram)

(i) Cut two lengths a and two widths b.  Join them to make the base rectangle.

(ii) Join the diagonals to find the middle and make a temporary wire for the height h. This fixes the vertex.

At this point the five points of the pyramid are all fixed.

(iii) You can cut four wires to join the base to the vertex and the model is complete.

It is not necessary is say how long the red lines for the slant heights are because they are already there, whatever size they need to be to join the midpoints of the base to the vertex.  Just choosing a length for these red lines is not an option.  Their lengths can be calculated using Pythagoras' theorem.  Furthermore, with a rectangular base the two slant heights will not be the same, so giving a single slant height value is only possible where the base is a regular polygon.  A rectangle is not a regular polygon.

This is why I have had such a problem with the slant height values given.  The pyramids described cannot exist because those slant height values won't work!

Sorry for the rant, but I felt I had to get that off my chest.  I feel better.  If that's leaving you worried and confused I apologise, but I have to take account of the possibility that other members of the forum may be reading this thread and I don't want them being taught incorrectly.

So now, back to the problems.  You can, of course, ignore all I have just said, and concentrate on getting the 'right' answers.  (Anyway, once you have a volume, you'll know which answer to choose, without having to calculate the lateral areas at all.    This is another criticism whoops, I'd better move on!)

The formula for the volume is

You have done Q6 volume correctly.

Their formula for lateral area is

So what you need to do is

(i) Add a + b + a + b to get the perimeter (distance around the base).

(ii) Calculate 1/2 of this and multiply by the slant height.

You can be fairly confident you have the right result if you can choose a single multi-choice answer that fits both the volume and area you have worked out.

Good luck.

Bob

anonimnystefy
2013-09-23 09:47:29

It truly is. The way you two tumble down those problems is amazing!

demha
2013-09-23 09:10:44

It's interesting to see two math geniuses at work

The shape is a pyramid with:

6. a rectangular base with a width of 4
A Lateral area: 120; Volume: 98
B Lateral area: 192; Volume: 76
C Lateral area: 240; Volume: 51
D Lateral area: 176; Volume: 33
E Lateral area: 288; Volume: 75
F Lateral area: 100; Volume: 64

So this is what I did. First I got the area of the rectangle:

a = 6 x 4
a = 24

v = 1/3 x 24 x 8
v = 64

That's what I'm getting for the volume.

As for the lateral area, would I have to do:
2 x 6 x 8
2 x 4 x 8

Get the answers for these, add them together to get the perimeter and then move on?

anonimnystefy
2013-09-23 06:00:13

Huh? I'm not sure what to make of your reply. I don't know how you will proceed when their questions are incorrect.

bob bundy
2013-09-23 05:58:17

Thank you so much.  It was driving me mad because I wasn't getting the right volume ... but, somehow, just having you say that has re-aligned my brain correctly to answer A too.  Oh joy!  Just got to square these formulas with the warped non Euclidean space that they occupy and I'm there.  Many, many thanks for your input.    I think I'm OK to proceed now.

Bob