Q&A - PSLE Math

[Winx5015]

Hi,can anyone help me solve the following questions.


1)There were a total of 800 paper clips in 3 containers, A, B and C.Alex transferred 3/8 of the paper clips from container A to container B.He then transferred 40 paper clips from container B to container C.As a result, the number of paper clips in container C is 1/5 the number of paper clips in container A There were 264 paper clips in container B at first. How many paper clips were there in container A at first?

2)The distance between point A and point B of an island is 50km.At 11am, Afiq left point A and cycled towards point B.Benny left point A half an hour later and cycled towards point B.Benny’s cycling speed was 4km/h faster than Afiq’s.At 1pm,Benny caught up with Afiq.When Benny was 10km away from point B,he stopped to wait for Afiq.
a)What was Benny’s speed?
b))How far was Afiq from Benny when Benny stopped to wait for him?

3)Mrs Gan baked 720 more chocolate cookies than vanilla cookies.She sold 3/4 of the chocolate cookies and 3/5 of the vanilla cookies.In the end, she had 60 more vanilla cookies than chocolate cookies left. What fraction of the cookies left were chocolate cookies?Express your answer in its simplest form.

Thanks:)

[Winx5015]

http://i47.tinypic.com/2ebbciv.jpg\">


How to solve this question? Help :imdrowning:

[tianzhu]

Michaelia0816:

Hi!

My teacher had assigned our math class' pupils to do a question without using Guess and check. I stuck at the second step, my first step is 192cm-129cm=63cm.

When Mr Lim measured and recorded the height of these children, he wrongly recorded one child's height as 192cm when it should have been 128cm.As a result, Mr Lim calculated the average height as 124.4cm. How many children were there in the group?

ASAP!

Hi girl

I’ve seen another similar question, but with the information highlighted in pink.

The average height of a group of children was 139.4cm. When the height of these children was measured and recorded, one child's height was wrongly recorded as 192cm when it should have been 129 cm. As a result, the average height of this group of children was calculated as 142.4 cm. How many children were there in the group?

Please help to confirm your question first.

Best wishes

[Michaelia0816]

tianzhu:

Michaelia0816:

Hi!

My teacher had assigned our math class' pupils to do a question without using Guess and check. I stuck at the second step, my first step is 192cm-129cm=63cm.

When Mr Lim measured and recorded the height of these children, he wrongly recorded one child's height as 192cm when it should have been 128cm.As a result, Mr Lim calculated the average height as 124.4cm. How many children were there in the group?

ASAP!

Hi girl

I’ve seen another similar question, but with the information highlighted in pink.

The average height of a group of children was 139.4cm. When the height of these children was measured and recorded, one child's height was wrongly recorded as 192cm when it should have been 129 cm. As a result, the average height of this group of children was calculated as 142.4 cm. How many children were there in the group?

Please help to confirm your question first.

Best wishes

Yes, this question is also found in Psle booklet.
It meant that the correct average height of them is 139.4cm not 142.4cm

[tianzhu]

Shimmer:

Hi I need help. Thanks


There are two bag of stones labeled A and B. In bag A ,there are 350 black stones and 500 white stones. In bag B , there are 400 black stone and 100 white stones. How many black and white should be transfer from bag B to bag A so that 50% of the stones in bag A and 75%of those in bag B are black?

Hi

There are different approaches; you may solve it pictorially, by units and parts or letters of the alphabet.

Number of black stones ------ 350 + 400 ------ 750

Number of white stones ------- 500 + 100 ------ 600

Bag A

Black: White ------ 1u:1u (50% black, 50% white)

Bag B

Black: White ------ 3p:1p (75% black, 25% white)

2p -------- 750 – 600 ------150

1p ------- 75

3p ------- 225

1p -------- 75

Number of black stones transferred out ------ 400 – 225 ------- 175

Number of white stones transferred out ------ 100 – 75 ------- 25

Best wishes

[tianzhu]

Michaelia0816:

Yes, this question is also found in Psle booklet.
It meant that the correct average height of them is 139.4cm not 142.4cm

Hi

If 139.4 is in the question, then the solution is

142.4 - 139.4 ------ 3

129 – 129 ------- 63

63/3 ------- 21 (number of children)

Best wishes

[MathIzzzFun]

Winx5015:

http://i47.tinypic.com/2ebbciv.jpg\">


How to solve this question? Help :imdrowning:

http://i46.tinypic.com/350whdu.png\">

cheers.

[tianzhu]

Winx5015:

3)Mrs Gan baked 720 more chocolate cookies than vanilla cookies.She sold 3/4 of the chocolate cookies and 3/5 of the vanilla cookies.In the end, she had 60 more vanilla cookies than chocolate cookies left. What fraction of the cookies left were chocolate cookies?Express your answer in its simplest form.

Hi

You may use MD or units.

chocolate cookies

At first ------- 20 units + 720

Sold ------- 15 units + 540

Left -------- 5 units + 180

vanilla cookies

At first ------- 20 units

Sold ------- 12 units

Left -------- 8 units

In the end, she had 60 more vanilla cookies than chocolate cookies left.

8 units ------- 5 units + 180 + 60

Please carry on from here.

Best wishes

[tianzhu]

Winx5015:

http://i47.tinypic.com/2ebbciv.jpg\">


How to solve this question? Help :imdrowning:

Hi

Another approach is to find the difference in areas between two squares.

If the use of calculators is allowed, it’s not too tedious to get the answer by “SL”.

Take for example, if 1 square is 10 cm, the other is 4 cm, find the difference in two square numbers.

Do a listing and find the numbers which match the given conditions.

Best wishes

[Zhu99]

Zhu99:

Shimmer:

3)Owen made 100 sandwich for $100.Chicken are sold for $5 each, fish are sold for $2 and plain are sold for $0.10.How many sandwich did she ??? for each flavor ?

Assume she sold 70 plain sandwich --- 70 x 0.10 = $73 [We need to make an intelligent guess. We may start with 80 ---- but will not get whole number for chicken and fish sandwiches]

100 - 7 = $93

100 - 70 = 30 --- No. of chicken and fish sandwich

30 x 2 = $60 --- if 30 fish sandwich

93 - 60 = $33 --- Amt short

5 - 2 = $3 --- Amt increase if convert 1 fish sandwich to 1 chicken sandwich

33/3 = 11 --- No. of chicken sandwich

30 - 11 = 19 --- No. of fish sandwich

(70 x 0.10) + (19 x 2)+ (11 x 5) = $100 [Check and confirm correct]

70 + 19 + 11 = 100 sandwich [Check and confirm correct]

She sold 70 plain, 19 fish and 11 chicken sandwiches.

5 C + 2 F + 0.1 P ---> 100 --- Amt collected

C + F + P ---> 100 --- No. of sandwich
5 C + 5 F + 5 P ---> 100 x 5 = 500

3 F + 4.9 P ---> 500 - 100 = 400 --- Get rid of 1 unknown (C)

F = (400 - 4.9 P)/3

For P = 100 and 90, F is negative.

For P = 80, F is not a whole number

For P = 70, F = (400 - 4.9 x 70)/3 = 19

C = 100 - 70 - 19 = 11

5 x 11 + 2 x 19 + 0.1 x 70 = $100 (Confirm correct)

She bought 11 chicken, 19 fish and 70 plain sandwiches.