Q&A - PSLE Math

[Muffins]

tianzhu:

Hi Muffins


Thank you for your offer.I understand your solution.

You have assumed that the unit of measures for both ratios is the same.

I appreciate your well wishes.May all PSLE kids be abundantly blessed with fruitful results.

Best wishes

No worries, Tianzhu,
Hoping all children bear the fruits of their labour too!

[Tang]

Praise:

Hi,


Can someone help to solve the following questions :-

1) There are some black and white marbles in a bag. If 20 black marbles are removed from the bag, the total number of marbles left will be 7 times the number of black marbles left. If 50 white marbles are removed from the bag, the total number of marbles left will be 5 times the number of black marbles left. How many marbles are there in the bag?

B -> 1u + 20
W -> 6u

B -> 1p
W -> 4p + 50

1u + 20 = 1p
4p = 4u + 80

6u = 4p + 50
6u = 4u + 80 + 50
2u = 130
1u = 65

7 x 65 + 20 = 475 marbles

There were 475 marbles in the bag.

[youngmum]

Thanks small. It’s not that i do not know that a triangle is 1/2 base x height. It’s just that at first i cannot see that the unshaded part is actually made up of half the rectangle. But now i get it already. Thanks. Thanks to all who helped me.

[Muffins]

youngmum:

small:

Please invert the diagram and take a look, it will be more clear.
The base of two triangles is 45 cm and the height is 22cm, thus their area:
1/2 x 45 x 22 which will be same as half of rectangle (area of rectangle = 45 x 22 )

i cannot see it

Hi youngmum,
please refer to image below.
As you can see, triangle PVR and triangle QVS make the length of the full rectangle, so together, their areas must make half of the rectangle. However, you must minus off the overlapping figure, which is 75 cm². That is the unshaded area. Then, you take the rectangle's full area, and minus the unshaded area from it and you have the shaded area.

Then you just put them in ratio form, and bring it down to its simplest terms, in this case, 19:14.

Quite a challenging problem on first sight, but it gets easier once you read the problem and figure out the relationships between everything in the figure.



http://farm3.static.flickr.com/2547/3984945203_a6bc525a6c_o.jpg\">

[Muffins]

James Ang:

Many of them will score A* for tomorrow's Maths paper because of the good habit of \"checking answers with calculator\" they have picked up.

Hi James, that is not necessarily true, you know. If they worked out the sum wrongly or, in their haste, punch in the wrong numbers on their calculators, calamity will befall!

[Muffins]

Maths PSLE paper is going to commence in about 14 hours, I can't think abut it, but I have to. AAAAAAAAAAAARGH! :!: :nailbite:

[James Ang]

Muffins:

James Ang:

Many of them will score A* for tomorrow's Maths paper because of the good habit of \"checking answers with calculator\" they have picked up.

Hi James, that is not necessarily true, you know. If they worked out the sum wrongly or, in their haste, punch in the wrong numbers on their calculators, calamity will befall!

Don't worry, many of the students are seasoned and bound to do very well for the PSLE. I am glad tomorrow is finally the Maths paper.

[Muffins]

Maths papers finished.. Am told that it was a killer paper. Many questions were hard and GEPers could also not finsih some of them. Only good thing is that if it was a hard paper and results are average all-round, then T-Scores would still be quite high.

[Jennifer]

Muffins:

Only good thing is that if it was a hard paper and results are average all-round, then T-Scores would still be quite high.

[parent135]

the paper is super easy and i finish everything in 1h 15 mins :lol: