Q&A - PSLE Math

[cimman]

Beikiasu:

3) The ratio of Jamal's mass to Katty's mass is 4:5.Jamal's mass is increased by 40% and Kathy's mass is decreased. What percentage of kathy's mass must be decreased so that thier total mass remains the same?TaoNan, 2011, Question 12, 4 mark, Ans:32%

the key thing about percentage problem is to know where to put the 100% or the base. It is not immediately obvious where the base is. Language skills and general knowledge here will help. Luckily, the vocabulary used in percentage problems are not that wide, so it is possible to memorize some key words and infer where is the 100%. In the above problem, the word \"by\" is commonly used in problem sums. ie. increased by.... the value that comes after this is the Transfer value, not the After value. Just memorize \"by\" = Transfer value.

Black fonts denote values transferred directly from the problem sum. Red fonts denote derived values.
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since the Total value remains the same, then the Total Transfer value = 0.
To get Total Transfer value = 0, Kathy Transfer value must be the same as Jamal's Transfer value, but with the opposite sign.

[mrsoon]

Fiona is 3 kg lighter than Eliza and 7 kg heavier than Tina.

If Fiona is j kg, find the total weight of the 3 girls.

This problem sum is taken from last year CA1 paper from a school.
The working j + (j + 3) + (j - 7) = 3j + 3 - 7
This will result in dealing with negative number.
Is this in the PSLE syllabus?

[cimman]

altp10:

Hi. I need help with the following Speed question.


Joel & Cliff ran a 100m race in which Joel crossed the finishing line just as Cliff reached the 90m mark.
a) Since Joel won the first race by 10m, he decided to start the second race 10m behind the starting line. Both boys ran at the same speed as in the first race. Who won the second race?
b) In the third race, Cliff started 10m ahead of the starting line. Again assuming that both boys ran at the same speed as in the first race, who was the winner of this race?

Thank you in advance.

in all speed problems, it is important to note that only 1 clock is used to measure time. As such, the key issue in speed problems is to know when to start and stop time measurement. Time is related to distance. For a given time, the distance traveled must be known. In more difficult speed problems, the start time and end times are vague and must be inferred based on logical reasoning and general knowledge. Luckily, there are only a few scenarios, so they can easily memorized.
In this case, general knowledge is called on to infer that both boys started the race at the same time. This is a simple inference, but nonetheless, it has to be noted it is an inference as it is not explicitly stated.

Speed problems are very similar to Rates problems as both deals with time. The difference between Rates and Speed is that Rates can be added (ie. Tap A and Tap B are turned on at the same time. John and Peter worked on the same Job at the same time), while Speed cannot.

In most Speed/Rates problems, there is a setup statement which tells us what is the rate or speed of the relevant objects. Thereafter, the rates or speed value do not change, unless it is explicitly stated. Learn to recognize the setup statements in each problem.
The first race is the setup statement, giving us information on the speed of Joel and Cliff. Thereafter, we copy the speed values to the 2nd and 3rd race.

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[Musicstar]

Please help to solve the question. Thank you.

[Beikiasu]

Hi, can someone help me to solve this problem sum?


1) William’s salary of $4800 was 20% more than Kate salary. They resigned and joined another company. In the new company, they were given the same percentage increase in their salaries. If the difference in their salaries is now $1200, what is the percentage increase? MB, 2011, Question 15, 4 mark, Ans: 50%

2) Xiaoming, Yanli and Zen went to a restaurant to have their lunch together. Each of them paid a different amount for their meals. Xiaoming paid 3/5 of what Yanli and Zen paid. Yanli paid 40% of what Xiaoming and Zen paid. If Zen paid $3 more than Yanli, how much did Xiaoming pay for his meal? Ai Tong, 2011, Question 10, 3 mark, Ans: $21.

3) On Saturday, there were 50 more females than males at a concert. On Sunday, the number of females increased by 10% and the number of males decreased by 20%, resulting in 625 people at the concert. Each ticket cost $25.How much money was collected on Saturday? Ros, 2011, Question 17, 5 mark, Ans:$16250.
Thanks.

[tianzhu]

Beikiasu:

Hi, can someone help me to solve this problem sum?


1) William’s salary of $4800 was 20% more than Kate salary. They resigned and joined another company. In the new company, they were given the same percentage increase in their salaries. If the difference in their salaries is now $1200, what is the percentage increase?

Hi

Before resignation

William ---- 6u ----- 4800

Kate ----- 5u ----- 4000

Difference ----- 800

After resignation, their difference is 1200

Percentage increase ----- 400/800*100% -----50%

Best wishes

[tianzhu]

Beikiasu:

2) Xiaoming, Yanli and Zen went to a restaurant to have their lunch together. Each of them paid a different amount for their meals. Xiaoming paid 3/5 of what Yanli and Zen paid. Yanli paid 40% of what Xiaoming and Zen paid. If Zen paid $3 more than Yanli, how much did Xiaoming pay for his meal? Ai Tong, 2011, Question 10, 3 mark, Ans: $21.

Hi

X:(Y+Z) ----- 3:5(8) ----- 21:35(56)

Y:(X+Z) ----- 2:5(7) -----16:40(56)

Make the total units the same.

X ----- 21u

Y-----16u

Z ----- 19u

3u ----- 3

1u ----- 1

X paid 21u or $21.

Best wishes

[tianzhu]

Beikiasu:

3) On Saturday, there were 50 more females than males at a concert. On Sunday, the number of females increased by 10% and the number of males decreased by 20%, resulting in 625 people at the concert. Each ticket cost $25.How much money was collected on Saturday? Ros, 2011, Question 17, 5 mark, Ans:$16250.

Hi

Saturday

Female ----- 10u + 50

Male ----- 10u

On Sunday, the number of females increased by 10% and the number of males decreased by 20%, resulting in 625 people at the concert.

Sunday

Female ----- 11u + 55

Male ----- 8u

19u + 55 ------ 625

1u ------- 30

On Saturday

Female ----- 10u + 50 -------350

Male ----- 10u ------300

Amount of money collected on Saturday ------ 650*25 ------ 16250

Best wishes

[Beikiasu]

tianzhu , :thankyou:


1) Willian & Kate
How you know 20% more is 6u & 5u?

3) Female & Male
Your eye so sharp, straight away you can see 10u. I tried drawing model but couldn't find the answer.

[tianzhu]

Beikiasu:

tianzhu , :thankyou:


1) Willian & Kate
How you know 20% more is 6u & 5u?

Hi

Just curious, is this question asked by the PSLE kid or the mummy?

Best wishes