Q&A - PSLE Math

[yomemai]

Workshops are also at HCI during the open house this year

[ksasalways]

yomemai:

Workshops are also at HCI during the open house this year

???the above workshop is organised to prepare parents and child for the coming PSLE. it is run over two different workshops and cover different topics.

[Michaelia0816]

Need help with a question and would like to ask which the answer. It worth 2 marks and is found in the last question of booklet A paper 1.


How many 2-digit even numbers can be formed with digits 2,3,4 if the digits can be repeated in each number formed?

1)6
2)8
3)9
4)12
Pls Tell why too.

[Neat]

MathIzzzFun:

Neat:

Hi!


I need explanation on the following question:

A large warehouse had a total of 2180 black, red and white T-shirts for sale. The ratio of the number of black T-shirts to the number of red T-shirts was 3:1. After 2/5 of the black T-shirts, 1/3 of the white T-shirts and none of the red T-shirts were sold on the first day, there were 1504 T-shirts left. How many red T-shirts did the warehouse have at first?

B : R : W Total
Before 3 : 1 : ? 2180
Sold -2/5 0 -1/3 676
After 3/5 1 2/3 1504

The working given in the paper is 6u + 1p = 676
12u + 2p = 676 x 2 = 1352
14u + 2p = 1504
2u = 1504-1352 = 152
5u = (152/2) x 5 = 380

My question is why 6u + 1p = 676? I thought we should find the
common factor for 2/5 and 1/3?

Please enlighten.
Thanks

Hi

hope this helps..

At first --- Black : Red : White = 15u : 5u : 3p
Sold --- Black : Red : White = 6u : 0 : 1p ---> 6u + 1p = 2180-1504 = 676
Left --- Black : Red : White = 9u : 5u : 2p --> 14u + 2p = 1504

cheers.

[quote]Hi! MathIzzzFun

Thanks for the clear explanation!
Must really know how to twist and turn!

:thankyou: [/quote]

[Flipper123]

Please help. Thank you.

http://i48.tinypic.com/34q0b42.jpg\">
Sorry i have no ansewr at the moment.

[Michaelia0816]

Flipper123:

Please help. Thank you.

http://i48.tinypic.com/34q0b42.jpg\">
Sorry i have no ansewr at the moment.

Hi! I can give you clue since you are working on it now,
Clue:
Angle ABR can be transferred to PCQ to form a square.Good luck, I has done on a question similar to this, since the line at the bottom is in the same length.

[Flipper123]

i tried this way and got the area of ABXY as 2 x 144 but i can’t confirm the vertical rectangle XYZP. can help? thanks.

[Flipper123]

sorry, here is the label http://i46.tinypic.com/2143961.jpg\">

i tried this way and got the area of ABXY as 2 x 144 but i can't confirm the vertical rectangle XYZP. can help? thanks.

[Andrew Lee]

Flipper123:

sorry, here is the label http://i46.tinypic.com/2143961.jpg\">

i tried this way and got the area of ABXY as 2 x 144 but i can't confirm the vertical rectangle XYZP. can help? thanks.

http://i48.tinypic.com/5fkw2p.jpg\">
http://i45.tinypic.com/55qkwl.jpg\">
hello, need help here..

[cimman]

Flipper123:

sorry, here is the label http://i46.tinypic.com/2143961.jpg\">

i tried this way and got the area of ABXY as 2 x 144 but i can't confirm the vertical rectangle XYZP. can help? thanks.

here's one way of looking at this problem:
http://i49.tinypic.com/2af0ojr.png\">

from the diagram, it looks like a rhombus. So the first step is to find out if it is a rhombus. We add in some lines along the mid points ...
http://i47.tinypic.com/1j3k77.png\">
by reflecting along lines of symmetry (rhombus diagonal), we find that the sides are equal in length, or you can take it that since this is an isosceles triangle (30,30, 120), both sides are the same length. This allows us to work out all the other angles.

You'll find that the lines (in blue) cuts the rhombus into 4 smaller rhombus. The blue lines intersect each other at the center of the rhombus and also at the center of the equilateral triangle. Notice the diagonal that was added that splits the equilateral triangle into 2 equal parts. This can be seen from the relevant angles.

Next we focus on one of the smaller rhombus and notice that it is made up of 4 small triangles.
http://i47.tinypic.com/2lag7f5.png\">

if we tessellate the red triangle, we find that it fits nicely into the equilateral triangle, since the equilateral triangle is cut into 6 equal pieces by drawing lines from the mid point of the triangle to the center of the triangle.
So each small triangle is 144/6 = 24

http://i46.tinypic.com/syqmis.png\">

once we have the area of a small red triangle, the rest is straight forward.
The entire rhombus is made up of 4 small rhombuses. Each small rhombus is made up of 4 red triangles. Each small red triangle = 24cm2.
The entire figure is made up of 4 x 4 = 16 small red triangles.
Answer would be 16 x 24 = 384cm2

Just as an exercise, if you tessellate the red triangle along lines of symmetry, this is what you'll get:
http://i47.tinypic.com/331g4qt.png\">

alternatively, you can view the figure from the viewpoint of the equilateral triangle:
http://i45.tinypic.com/jv0qdd.png\">
the blue triangle is half the area of the equilateral triangle. The green area is the same as the blue area.