Q&A - PSLE Math

[abc_parent]

Thanks to Maths Monster!!

[abc_parent]

Hi everyone,

Q13,15 contain diagrams. Please help if you have the exam paper.

Q13) The diagrm below shows 3 identical circles embedded in a rectangle. Given that the length of the rectangle is 18cm, find the total area of the shaded parts. Use a calculator to obtain the value of pi. (Give your answer correct to 2 decimal places)

–> I don’t understand in the solution provided:
18cm / 3 = 6cm
Big triangle -> 18 x 6.5 = 54
6cm / 2 = 3cm
1 circle -> 3 cm x 3cm x pi = 9pi
54-9pi = 25.725 [why minus area of 1 circle only?]


Q14) Audrey and Belle have some money each. If Audrey spends $18 and Belle spends $24 each day, Audrey will still have $25 left when Belle has spent all her money. If Audrey spends $13 and Belle spends $30 each day, Audrey will still have $139 left when Belle has spent all her money. How much money do they have altogether?

Ans:$655

Q15)The series of figures below are made of cubes. Study the diagram below and answer the following questions.
(a) How many cubes will there be in Figure 6?
(b) Which figure will have 120 cubes?

Ans: 56
Ans: Figure 8

–> I don’t understand the series.Can someone explain, please?

Q17) Yusof has a total of 560 local and foreign stamps. After giving away 80% of the local stamps and 50% of the foreign stamps, he had 172 stamps left.
(a) How many local stamps did he have at first?
(b) How many foreign stamps did he give away?

Ans: (a) 360
(b) 100

[Maths Monster]

abc_parent:

Hi everyone,


Q17) Yusof has a total of 560 local and foreign stamps. After giving away 80% of the local stamps and 50% of the foreign stamps, he had 172 stamps left.
(a) How many local stamps did he have at first?
(b) How many foreign stamps did he give away?

Ans: (a) 360
(b) 100

Yusof has a total of 560 local and foreign stamps.
L + F =560

After giving away 80% of the local stamps and 50% of the foreign stamps, he had 172 stamps left.
1/5L + 1/2F = 172

If we multiply by 2:
2/5L + F = 344

We can see that:
3/5L = 560-344
L=360

F=200
He gave away 50% of the foreign stamps which is 0.5x200=100

[tianzhu]

Hi

Hope this helps.

http://farm5.static.flickr.com/4137/4773175314_04b721ac8f_b.jpg\">

Best wishes

[Maths Monster]

abc_parent:

Hi everyone,


Q14) Audrey and Belle have some money each. If Audrey spends $18 and Belle spends $24 each day, Audrey will still have $25 left when Belle has spent all her money. If Audrey spends $13 and Belle spends $30 each day, Audrey will still have $139 left when Belle has spent all her money. How much money do they have altogether?

Ans:$655

If Audrey spends $18 and Belle spends $24 each day, Audrey will still have $25 left when Belle has spent all her money.

Let u be the number of days in this case.

A [18u][25]
B [24u]

If Audrey spends $13 and Belle spends $30 each day, Audrey will still have $139 left when Belle has spent all her money.

A [18u-114][139]
B [24u]

The ratio of [18u-114] and [24u] is 13:30, we can write the equation:
(18u-114)x30 = (24u)x13
540u-3420=312u
228u=3420
u=15

Therefore,
A = 18u+25 = $295
B = 24u = $360
Total = $655

Check:
If Audrey spends $18 and Belle spends $24 each day, Audrey will still have $25 left when Belle has spent all her money.
A = (295-25)/18 = 15 days
B = 360/24 = 15 days

If Audrey spends $13 and Belle spends $30 each day, Audrey will still have $139 left when Belle has spent all her money.
A = (295-139)/13=12 days
B = 360/30 = 12 days

[Maths Monster]

Budo:

Hi need help in this question


Andrew and Brian had some money
If Andrew gave Brian $55, the ratio of Andrew to Brian amount is 3:5.
If Brian gave Andrew 20% of this money and $10, Andrew would have $108 more than Brian.
How much do Andrew and Brian have at first?

If Andrew gave Brian $55, the ratio of Andrew to Brian amount is 3:5.
A [3u]
B [5u]

At start,
A [3u+55]
B [5u-55]

If Brian gave Andrew 20% of this money and $10, Andrew would have $108 more than Brian. 20% of 55 + 10 = $21
A [3u+55+21] = [3u+76]
B [5u-55-21] = [5u-76]

We can write the equation:
3u+76-108 = 5u-76
2u = 44
u =22

Therefore, at first,
A = 3u+55 = $121
B = 5u-55 = $55
Total = $176

[hamsterss]

livewith_vanilla:

hamsterss:

[quote=\"ruyu\"]

[/quote]
Really? I saw the Maths Workbook 6B's answer key wrote the answer as :

1000+2000=3000km [Example]

Is it okay since the answer key in the Maths Workbook 6B wrote it this way?

One more :oops:

Can i just write :

100m + 3km = 3.1km? even though the unit is not the same?

Thanks

[ruyu]

hamsterss:

livewith_vanilla:

[quote=\"hamsterss\"]

[/quote]
sorry cannot. Marks will be deducted. You have to do something like this:

3km = 3000m

100m+3000m= 3100m

3100m=3.1km


Yeah this is the way. Dont need to write final statement waste time.Do live_vanillacake way

[angela]

Can anyone help in this question ( Raffles Girls 2009 SA1)?


Container A contains 250 red marbles and 200 blue marbles.
Container B contains 600 red marbles and 150 blue marbles.
How many red and blue marbles must be moved from Container A to Container B such that 25% of the marbles in Container A are red and 75% of the marbles in Container B are red?

Thanks

[tianzhu]

Hi

Hope this helps.
http://farm5.static.flickr.com/4122/4778205021_8f7608186f_b.jpg\">
Best wishes.