Q&A - PSLE Math

[wkong]

Hi all, have a question for you-


Chef John only has a 3-minute hourglass timer and a 5-minute hourglass timer. Write down a list of instructions to help Chef John time his cooking to exactly 7 minutes.

Thanks in advance.

[stary]

Hi all,


Need help on average.

The pupils in 2 classes, 1A and 1B did a Mathematics test. The average score of class 1A, which had 24 pupils, was 87. The average score of Class 1B was 80. If the average score of the two classes was 83, how many pupils were there in Class 1B?

Ans key says the ans is 32, but I do not know how to get the explanation for the workings...

Can someone explain to me the bold and underlined part?

Total score of class 1A -> 87 x 24 = 2088
83 x 24 = 1992
2088 - 1992 = 96
83 - 80= 3
96 / 3 = 32

Appreciate your assistance.

[stary]

wkong:

Hi all, have a question for you-


Chef John only has a 3-minute hourglass timer and a 5-minute hourglass timer. Write down a list of instructions to help Chef John time his cooking to exactly 7 minutes.

Thanks in advance.

Legend:
A = 3-min hour glass
B = 5-min hour glass

Step 1: Start both hour glasses together.
Step 2: When A finishes timing, turn it round again.
Step 3: When B finishes timing, turn A again.
Step 4: Presto! You've got your 7th min!

[MathIzzzFun]

stary:

Hi all,


Need help on average.

The pupils in 2 classes, 1A and 1B did a Mathematics test. The average score of class 1A, which had 24 pupils, was 87. The average score of Class 1B was 80. If the average score of the two classes was 83, how many pupils were there in Class 1B?

Ans key says the ans is 32, but I do not know how to get the explanation for the workings...

Can someone explain to me the bold and underlined part?

Total score of class 1A -> 87 x 24 = 2088
83 x 24 = 1992
2088 - 1992 = 96
83 - 80= 3
96 / 3 = 32

Appreciate your assistance.

Hi

http://i52.tinypic.com/2r2ryb4.jpg\">

cheers.

[MathIzzzFun]

Hershey:

MathIzzzFun:

[quote=\"Hershey\"]Dear Parents, hope someone can help to solve this 2 questions from 2010 Catholic High Prelim paper.


1) At a conference made up of speakers and participants, there were 20% more men than women. the ratio of male speakers to female speakers was 8:5. There was an equal number of male and female participants.

a) Find the ratio of male speakers to male participants at the conference.

b) Halfway, 40 male participants left the conference and another 60 male participants joined the conference. in the end, there was 3/4 as many male participants as female participants remaining behind. How many speakers were there at the conference.


2. At 9am, John was cycling from Point A to Point B. At the same time, Mary was cycling from Point B to Point A using the same route as John. Cycling at a speed of 4km/h faster than Mary, John would pass Mary 300m away from the midpoint.

a) what time did they pass each other?

b) If John took another 3 mins to reach Point B, what time would Mary reach Point A?

Really don't understand why kids are being drill on this kind of questions...even adults need to think....

Thanks.

Hi

For Q1(b), the question should be \"Halfway, 40 male participants left the conference and another 60 female participants joined the conference.\"

http://i52.tinypic.com/280ld0g.jpg\">

For Q2, refer to http://www.kiasuparents.com/kiasu/forum/viewtopic.php?f=27&t=280&start=3470

cheers.

Thank you so much. Its my typo error on Q1b. :imsorry:[/quote]u r welcome

cheers.

[stary]

MathIzzzFun:

stary:

Hi all,


Need help on average.

The pupils in 2 classes, 1A and 1B did a Mathematics test. The average score of class 1A, which had 24 pupils, was 87. The average score of Class 1B was 80. If the average score of the two classes was 83, how many pupils were there in Class 1B?

Ans key says the ans is 32, but I do not know how to get the explanation for the workings...

Can someone explain to me the bold and underlined part?

Total score of class 1A -> 87 x 24 = 2088
83 x 24 = 1992
2088 - 1992 = 96
83 - 80= 3
96 / 3 = 32

Appreciate your assistance.

Hi

http://i52.tinypic.com/2r2ryb4.jpg\">

cheers.

Thanks MathIzzzFun! :thankyou:

[pensiveowl]

Tang:

tianzhu:

[quote=\"trytry\"]A courier company charged $25 for every large parcel and $15 for every

small parcel delivered safely. However, a penalty of $50 was charged for
every damaged parcel regardless of size.
This month, the company delivered 120 parcels of which 1/4 of them were
small parcels. It collected a total of $2000 after paying a penalty for
an equal numbers of large and small parcels.
How many large pacels were delivered safely?
(Nanyang 2010 SA1 P2 Q12)
The answer provided was 83. But mine is 85. Which is correct?

Hi

83 is correct.

Best wishes

Hi,

85 is the correct answer.


85 x 25 = 2125

25 x 15 = 375

2125 + 375 = 2500

5 + 5 = 10

10 x 50 = 500

2500 - 500 = $2000 (amount collected).



Solution as follows:

120/4 = 30 small parcels

120 - 30 = 90 large parcels

Assume all dilivered safely, amount collected

90 x 25 + 30 x 15 = $2700



2700 - 2000 = $700 (too much)


Removing 1 large and 1 small parcels,

amount collected less by 25 + 15 = 40

penalty paid 50 + 50 = 100


Total amount reduced by 40 + 100 = $140


700/140 = 5, i.e. 5 large and 5 small parcels damaged.

90 - 5 = 85 large parcels were delivered safely.[/quote]I had a little trouble understanding this.. until I wrote it out like this:
The company delivered 120 x ¼ = 30 small parcels and 90 large parcels.
It should have collected [(30 x 15) + (90 x 25)] = $2700
It didn’t get paid for items damaged, moreover was charged $50 for @ damaged.
For each pair of large and small item damaged:
It didn’t collect 25 + 15 = 40
On top of this, it was charged 50 + 50 = 100
Thus, it lost $140 ($40 + $100) for each pair of large and small items damaged.
700/140 = 5
Thus, 5 large and 5 small items were damaged.
90 – 5 = 85
85 large parcels were delivered safely.

[stary]

Hi all,


Have a question...

Ali and Baba ran in a race. When Baba had completed the race, Ali had only run 5/8 of the distance. Baba's speed was 75 m/min faster than Ali's speed. Both of them did not change their speeds throughout the race.
Waht was Ali's speed in m/min?

Appreciate your help... :?

[wkong]

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[wkong]

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