Q&A - PSLE Math

[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

[Essential]

Hi anyone can help this question? A car left town A at 0800 and travelled to Town B at an average speed at 60 km/h. at the same time , a lorry left town B for Town A. At 11 30 , the car and the lorry were 85 km apart after passing each other earlier . If the car arrived at Town B at 1300 , at what time would the lorry arrived at Town A?

[Essential]

Thank u Tianzhu you are super fast . May I know are u a tutor?

[tianzhu]

Essential:

Hi anyone can help this question? A car left town A at 0800 and travelled to Town B at an average speed at 60 km/h. at the same time , a lorry left town B for Town A. At 11 30 , the car and the lorry were 85 km apart after passing each other earlier . If the car arrived at Town B at 1300 , at what time would the lorry arrived at Town A?

Hi

It’s useful to have a pictorial representation for Speed questions.

I’ll just provide some pointers.

Draw a bar, and label A and B at both ends.

At 1130, the car is at point C and the lorry is at point D.(D is nearer to A).

From 0800 to 1130, the car covered 60*3.5 ----- 210 km (A to C)

From 1130 to 1300, the car covered 60*1.5 ----- 90 km (C to B)

Distance (B to D) travelled by lorry from 0800 to 1130 ------ 90 + 85 ------ 175 km

From here, lorry’s speed ------ 175/3.5 ------- 50 km/h

From point D to A, the lorry covered (210 – 85) which is 125 km

Time taken by lorry ------125/50 ------ 2.5 h

From 1130h, add 2.5h, this gives 1400 h

Best wishes