Q&A - PSLE Math

[MathIzzzFun]

danishcookies:

1) In a school choir, the ratio of the number of boys to the number of girls in is 2:3. 1/4 of the boys and 1/2 of the girls wear spectacles. If there are 48 pupils who wear spectacles, how many pupils are there in the choir?


2) John has $28 more than Peter. 1/3 of John's money is equal to 4/5 of Peter money. Find John money?

Hi
1)
Boys -->12 units, Girls --> 18 units, total 30 units
Boys with specs --> 3 units
Girls with specs --> 9 units
12 units --> 48, 1 unit --> 4

Total number of pupils in choir --> 30 x 4 = 120

2)
4/5 Peter's money = 1/3 John's money = 4/12 John's money
John's money --> 12 units
Peter's money --> 5 units
7 units --> $ 28, 1 unit --> $4
John's money --> 12 x $ 4 = $ 48

cheers.

[peggy]

Hi Small,


I understand that my salary is 20% less than my brother, but you get 120/0.8?

[small]

peggy:

Hi Small,


I understand that my salary is 20% less than my brother, but you get 120/0.8?

Hi Peggy,

HTH..

Used sister as 100% thus my salary is 100 x 1.2 = 120

my salary = 80% or 0.8 of brother's salary
my salary / 0.8 = brother's salary

[peggy]

Hi Small,


Thanks for your quick response.
Good nite!

[small]

peggy:

Hi Small,


Thanks for your quick response.
Good nite!

You are welcome, peggy..

Good night to you as well.

[Neat]

Hi morning,


Please assist on the following question:

30% of the books in a library were fiction, 25% of them were non-fiction and the rest were reference books. After 200 more fiction and non-fiction books were ordered, the percentage of the reference books in the library decreased to 40% and the number of fiction books increased by 10%. How many non-fiction books were ordered?

Thanks vm

[tianzhu]

Neat:

Hi morning,


Please assist on the following question:

30% of the books in a library were fiction, 25% of them were non-fiction and the rest were reference books. After 200 more fiction and non-fiction books were ordered, the percentage of the reference books in the library decreased to 40% and the number of fiction books increased by 10%. How many non-fiction books were ordered?

Thanks vm

Hi

You may use MD or UM.

FB:NFB:RB ----- 30%:25%:45% -------6u:5u:9u

RB remained unchanged.

40% ------ 9u
60% ------- 13.5u

13.5u ------- 11u + 200
1u ------ 80

Number of FB at first ------6*80 -------480
Number of FB in the end ------ 528 (10% increase)

Number of FB and NFB in the end ------13.5*80 ------1080
Number of NFB in the end ------- 1080 – 528 ------552

Number of NFB at first ------ 5*80 ------- 400
552 – 400 --------152

Number of NFB ordered ------152

Best wishes

[mathfreak]

Superbugs:

mathfreak:

[quote=\"Superbugs\"]Nan Hua CA1 P6 2011

Q14.
My salary is 1/5 more than my sister but 20% less than my brother. If our total salary is $11,100, what is my sister's salary?

If Me=100%
Brother =120%
Sister=80%
80/300x11,100=2960
but answer is $3000?
Pls assist. Tks

Actually, if Me is 100%, Sister is not 80% (this means \"Me\" had 1/4 more than Sister), but instead is 100%*5/6=83 1/3%. This is so that 1/5 of Sister added to Sister will give \"Me\".
Brother is also not 120% (this means \"Me\" had 16 2/3% less than Brother), but instead is 100%*5/4=125%. This is so that 20% of Brother subtracted from Brother will give \"Me\".
The total would be 308 1/3%, which means 83 1/3% is $3000.

Tks a lot! I realised my mistake.[/quote]You're welcome.

[tianzhu]

Superbugs:

Nan Hua CA1 P6 2011

Q7:
I have some red and blue ribbons in a bottle.
If I add in 20 red ribbons, 60% of my ribbons are blue.
If I add in another 60 blur ribbons, 75% of my ribbons are blue.
How many ribbons have I in the bottle?
Please help with this question. Tks

Hi

This question has been floating around in forums regularly.

It was discussed in our earlier posts. Depending on one’s interpretation of the word another in the second condition, one may end up with 180 or 80.

It’ll be helpful if current PSLE students or their parents help to clarify with their school teachers on this question.

Condition1
Red : Blue -------- change add 20 red ribbons
2u:3u

Condition 2
Red : Blue -------- change add 60 blue ribbons
1p:3p

2u – 20 ------- 1p
3u + 60 -------3p

Equalising the parts

6u – 60 -------3p

3u + 60 ------- 6u - 60
3u ------ 120
1u ------ 40

Number of ribbons at first ------ (5*40) - 20 ------180

Best wishes

[notfreemom]

Hi, please help me with this question.


Evergreen School spent $9065 on some tennis rackets and badmintob rackets. The ratio of the number of tennis rackets bought to the number of badminton rackets bought was 5:7. A tennis rackets costs $13.30 more than a badminton racket. The total cost of the tennis racket was 17/20 of the total cost of the badminton rackets. Find the cost of the one such tennis racket.
Thanks.