Q&A - PSLE Math

[MathIzzzFun]

tech_nomax:

MathIzzzFun:

[quote=\"tech_nomax\"]At Station A, the ratio of the number of children to the number of adults on a train was 4:5. At the next station, 12 children alighted and 10 adults boarded the train. The ratio of the number of children to the number of adults on the train then became 7:10. How many children were on the train at first?

Hi

At first, Children : Adults --> 8u : 10u
In the end, Children : Adults --> 7u + 7 : 10u + 10
So, 8u - 12 = 7u +7
1u --> 19

Children, at first --> 8 x 19 = 152

cheers.

:thankyou: very much MathIzzzFun!

could you please let me know in line two, why to write
In the end, Children : Adults --> \"7u + 7 : 10u + 10\", instead of \"7u : 10u\".

Thanks in advance.[/quote]Hi

It is easier to see with a MD, so try drawing the model.
in the end,
10 adults boarded, so
total number of adults --> 10u + 10 = 10 x (1u + 1)
Since in the end, ratio of children : adults = 7 : 10
children --> 7 x (1u + 1) = 7u + 7

here's the MD...

http://i49.tinypic.com/jph1jr.png\">

cheers.

[brastilava]

Hi, please help in this question:


The figure below is made up of three triangles A, B, and C.
50% of Triangle A is shaded. 1/4 of Triangle B is shaded. 20% of Triangle C is shaded. The total area of Triangle A and Triangle B is 125% of the area of Triangle C. Express the area of Triangle A as a fraction of the area of Triangle B. Leave your answer in its simplest form.

http://i49.tinypic.com/ok7a7k.jpg

[MathIzzzFun]

brastilava:

Hi, please help in this question:


The figure below is made up of three triangles A, B, and C.
50% of Triangle A is shaded. 1/4 of Triangle B is shaded. 20% of Triangle C is shaded. The total area of Triangle A and Triangle B is 125% of the area of Triangle C. Express the area of Triangle A as a fraction of the area of Triangle B. Leave your answer in its simplest form.

http://i49.tinypic.com/ok7a7k.jpg

Hi

this was posted some time ago - http://www.flickr.com/photos/62167097@N02/6705370185/in/set-72157629872038060

cheers.

[tianzhu]

brastilava:

Hi, please help in this question:


The figure below is made up of three triangles A, B, and C.
50% of Triangle A is shaded. 1/4 of Triangle B is shaded. 20% of Triangle C is shaded. The total area of Triangle A and Triangle B is 125% of the area of Triangle C. Express the area of Triangle A as a fraction of the area of Triangle B. Leave your answer in its simplest form.

http://i49.tinypic.com/ok7a7k.jpg

Hi

A similar question has been discussed before.

Hope this helps.

Best wishes

http://farm8.staticflickr.com/7161/6707675849_d6e9dec552_z.jpg\">

[brastilava]

Thanks Tianzhu for your clear pictorial. I understand now.

[brastilava]

:thankyou: MathIzzzFun for your answer!

[dicoyote]

Hi All,


I have a difficulty in this question, seeking help, thanks in advanced

\"The average height of a group of children was 139.4 cm

When Mr Tan measured and recorded the height of these children, he wrongly recorded one child's height as 192 cm when it should have been 129 cm.
As a result, Mr Tan calculated the average height as 142.4 cm.

How many children were there in the group?\"

[pixiedust]

dicoyote:

The average height of a group of children was 139.4 cm


When Mr Tan measured and recorded the height of these children, he wrongly recorded one child's height as 192 cm when it should have been 129 cm.
As a result, Mr Tan calculated the average height as 142.4 cm.

How many children were there in the group?

I'll give this a try but I can't draw the nice diagrams

Right Average = 139.4cm
Wrong Average = 142.4cm
Difference = 142.4cm - 139.4cm=3cm

Right Height = 129cm
Wrong Height = 192cm
Difference = 63cm
--> this is what contributed to the difference in average.

Hence, the number of children = 63/3=21

==================================
Check :
Right total=21x139.4=2927.40cm
Wrong total=21x142.4=2990.40cm
difference in total = 63cm <right>

[Michaelia0816]

dicoyote:

Hi All,


I have a difficulty in this question, seeking help, thanks in advanced

\"The average height of a group of children was 139.4 cm

When Mr Tan measured and recorded the height of these children, he wrongly recorded one child's height as 192 cm when it should have been 129 cm.
As a result, Mr Tan calculated the average height as 142.4 cm.

How many children were there in the group?\"

Use guess and check method, remember the total average number difference is 63, good luck at finding, I already found out the answer, simple!

[dicoyote]

Hi pixiedust and Michaelia0816,


Nice one, thanks for the speedy response, will run through the given suggestion, hope I can understand