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## Friday, July 31, 2009

### Singapore Chinese Girls Sch 2008 PSLE Math Prelim Q42

In the diagram below, 75% of square Z is not shaded. The ratio of the area of square X to the area of square Y is 9:4. The ratio of the area of square Y to the area of square Z is 4:1.
a) What is the ratio of the area of square X to the area of square Z?
b) Find the ratio of the unshaded area of square Y to the unshaded area of square Z.

Solution

a)
X : Y : Z
9 : 4 : 1

X : Z

b)
Total Area
Y : Z
4 : 1
16 : 4

Y : Z
15 : 3 * (see explanatory notes below)

* Total Area (ratio) Y:Z is 4:1. 75% of Z is unshaded, hence for Z, 3 units out of 4. This means 1 unit is shaded. For Y, 16 units total less 1 unit shaded = 15 units unshaded. Hence, unshaded area is Y:Z ---- 15:3.

Anonymous said...

Science Time: When Raju blows into a balloon, the size of the balloon increases. Explain why the balloon becomes bigger.

Science Time: Give an example of micro-organism. State one way micro-organisms is useful to humans. Is there any website that give different examples of micro-organism and their usefulness or harmfulness to humans (suitable for PSLE level) ?

Science Time: Q: State the conditions required for seeds to germinate ? Which is the better answer ? A1: Seeds require air , water and warmth to germinate. A2: Seeds require oxygen, water and the right temperature to germinate.

Science Time: Alice filled an opening closed syringe with small pieces of a solid X. When the plunger is pushed, the volume in the syringe decreases. (a) Explain why the plunger can be pushed in (b) What could solid X be ? (c) State one property of solids.

Anonymous said...

Science: The air in Solid X has been compressed. Solid X could be a sponge.
2 Aug 09, 21:56
Science: We talk about shock absorber but I don't think we talk about heat absorber. It should be good or poor conductor of heat. A good conductor of heat will allow heat to pass through it easily while a poor conductor of heat will slow down the flow of heat through it.
2 Aug 09, 21:53
Science: Pl change human to plants.
2 Aug 09, 21:53
Science: Bacteria can be beneficial to human. Eg. bacteria that decay matter and help to break down into simpler substance which act as nutrients for plants.
2 Aug 09, 21:48
Science: "A1: Seeds require air , water and warmth to germinate. A2: Seeds require oxygen, water and the right temperature to germinate." Both answers will be acceptable.
2 Aug 09, 21:43
Science: What is a solid? Solid is any matter that has a definite shape and volume. Are plasticine and sponge solid? Yes they are. So they have definite volume. They also have definite shape, unless a force is applied on them.

Anonymous said...

There was a prelim question that goes like sth like this: Mary has some sweets. She gave away 1/3 of her sweets to her friend, 15 sweets to her brother and kept the half remaining sweets to herself. How many sweets does she have at first? The answer is 90 or 45?

Anonymous said...

Raju who was looking for his friend's flat took a lift to the 10th storey and walked 3 storeys by the staircase. Then he went up 2 storeys, down 5 storeys and up 4 storeys where he finally found the flat. On what storey was his friend's flat ?

Anonymous said...

Car A left Town X for Town Y while Car B left Town Y for Town X and both cars left at the same time. The ratio of their respective speed is 5 : 4 initially. After they passed each other, Car A reduced its speed by 1/5 while Car B increased its speed by 20 %. When Car A reach Town Y, Car B was still 25 km away from Town X. What is the distance between Town X and Town Y?

Anonymous said...

Question: If each pupil in the class sends a Chrismas card to every classmate, the total number of cards sent by all pupils will be 870. Find the number of pupils in the class.

Pattern: Using Pattern, n pupils each sends out (n-1) Christmas cards. n x (n-1) = 870. 30 x 29 = 870. So n = 30 pupils.