Q&A - PSLE Math

[Spongy]

Hi I need help in this question. Please help. Thanks.


1. 500 people paricipated in a contest. 105 of them were adults and the rest were children. 3/5 of boys and 5/7 of the girls were Singaporeans while the rest of the children were foreigners. There were 10 more foreign girls than foreign boys. How many Singaporean children were there?

[mumworks]

:thankyou: tianzhu

[tianzhu]

Winx5015:

Hi, need help for the following questions.


(1). There were 40 red pens and 45 blue pens in Stall A. Stall B had 50 red pens and 15 blue pens. How many red pens must be moved from Stall B to Stall A so that 50% of the pens in Stall A and 75% of the pens in Stall B are red?

Hi

This question touches on simultaneous concept.

You may use MD, “Units and Parts” or use letters of the alphabet to show the variables.

At first

Stall A
R:B ----- 40:45

Stall B
R:B ----- 50:15

In the end

Stall A
R:B ----- 1u:1u (50% of the pens in Stall A are red)

Stall B
R:B ----- 3p:1p (75% of the pens in Stall B are red)

1u + 3p ------ 90 (40+50)

1u + 1p ------ 60 (45+15)

2p ------- 30

1p ------- 15

Stall B
R:B ----- 45 (3*15):15 (1*15)

50 – 45 ----- 5

Number of red pens moved from Stall B to Stall A ------- 5

Best wishes

[tianzhu]

Spongy:

Hi I need help in this question. Please help. Thanks.


1. 500 people paricipated in a contest. 105 of them were adults and the rest were children. 3/5 of boys and 5/7 of the girls were Singaporeans while the rest of the children were foreigners. There were 10 more foreign girls than foreign boys. How many Singaporean children were there?

Hi

This question touches on simultaneous concept.

You may use MD, “Units and Parts” or use letters of the alphabet to show the variables.

Number of children ------- 500 – 105 ------ 395

Boys

Singaporean ------- BBB
Foreigner ------ BB

Girls

Singaporean ------- GGGGG
Foreigner ------ GG

GG ------ BB + 10
G ----- B + 5

BBBBB + BBBBBBBBBBBB + 35 -------- 395 (12B + 35 ------ 395)

B ------ 30
G ------ 35

Number of Singaporean children ----- 90 + 175 ------ 265

Best wishes

[tianzhu]

Michaelia0816:

Of thx Tianzhu and mathizzzfun! :thankyou:

Hi girl

Great, you got it.

So, I'll not be sending you any more information.

Best wishes

[tianzhu]

kiasuaunt:

Hi - don't understand this part: 7u+3u+30 = 480. How did u get +30 ? Sorry for being so slow.

Hi

Oh, this slide reminds me that I am one year older.

3 parts + 7 units ------- 480

1 part ------ 1 unit + 10

Hence, 3 parts ------ 3 units + 30

Best wishes

[tianzhu]

Shimmer:

One more question please !


Bottles A, B and C contains 2.03 litres of oil altogether. 1/5 of the oil in bottle A is transferred to bottle B, after that 1/5 of the oil in bottle B is transferred to bottle C. Now bottle A has twice the amount of oil in bottle B and bottle B has twice the amount of oil in bottle C.
A) How much oil was transferred from bottle A to B ?
B) How much oil was in bottle C at first ?

Hi

A neat way to do this question is to use MD. You may also work using units.

Due to time constraints, I’ll not be drawing it but will be providing some pointers.

Start with the end scenario and work backwards.

A ------ 4 units (boxes)
B ------ 2 units
C ------ 1 unit

7 units ------ 2.03
1 unit ------ 0.29

0.29 litres of oil was transferred from A to B

Now consider Bottle B

2 units ------ 0.58

After 1/5 of the oil in bottle B is transferred to bottle C, the amount of oil in B is 0.58 litres

4 parts ----- 0.58
1 part ----- 0.145

0.145 litres of oil was transferred from B to C

0.29 – 0.145 ------ 0.145

Amount of oil in bottle C at first ------ 0.145

Best wishes

PS

Amount of oil at first

A --- 1.45
B --- 0.435
C --- 0.145

[kiasuaunt]

tianzhu:

kiasuaunt:

3. There were 544 brownies and cupcakes for sale at a bakery. All the brownies at a bakery cost $488 more than all the cupcakes. After 4/5 of the brownies and 1/4 of the cupcakes were sold, there were twice as many brownies as cupcakes left. Each brownie cost 80 cents less than each cupcake. How much did each brownie cost ?

Hi

Please help to confirm.

Is it 488 or 448?

Brownies ------ 480*1.2 ------ 576

Cupcakes ------ 64*2 ------ 128

Difference ------- 448

Best wishes

Hi - yes, it's $448 - sorry.

:thankyou: for the solutions - will try to digest them now and teach my dd later. We've been keeping u very busy. Thanks again for your time and effort.

[Essential]

Hi Tianzhu, not sure this question any one asked before . Please kindly help us. The sum of 6 numbers is 624 . When a 7th number is added . The average of the numbers increases by 2. When a 8th number is added, the average of the 8 numbers increases by 2 again . Find the 8th number.

[tianzhu]

Essential:

Hi Tianzhu, not sure this question any one asked before . Please kindly help us. The sum of 6 numbers is 624 . When a 7th number is added . The average of the numbers increases by 2. When a 8th number is added, the average of the 8 numbers increases by 2 again . Find the 8th number.

Hi

For 6 numbers

Average ------ 624/6 ------ 104

For 7 numbers

Average ------ 106

Total ------ 106*7 ------- 742

For 8 numbers

Average ------ 108

Total ------ 108*8 ------- 864

The 8th number ------- 864 – 742 ------- 122

Best wishes