Q&A - PSLE Math

[ChiefKiasu]

youngmum:

Another Question - OMG.


The average number of letters in 6 magic spells is 9. Four of the magic spells are LUMOS, CRUICIO, PROTEGO and CONFUNDO. The 2 remaining spells have the same number of letters. How many letters does each of teh 2 spells have?

It's also a test of your Harry Potter knowledge. The correct spelling for the unforgivable spell is CRUCIO, ie. 6 letters.

So total number of letters in the 4 spells = 26.
Total number of letters in the 6 spells = 9x6 =54
So total number of letters in the remaining 2 spells = 54-26 = 28
So each remaining spell has 28/2 = 14 letters each

[youngmum]

ChiefKiasu:

It's also a test of your Harry Potter knowledge. The correct spelling for the unforgivable spell is CRUCIO, ie. 6 letters.

So total number of letters in the 4 spells = 26.
Total number of letters in the 6 spells = 9x6 =54
So total number of letters in the remaining 2 spells = 54-26 = 28
So each remaining spell has 28/2 = 14 letters each

piang. like that also can. gum sia leh.

[youngmum]

this question how?


The club has 1150 members. 20% of men and 25% of women are non professional photographers. a total of 250 members are non professional photographers. how many more men than women are there int eh club?

[lizawa]

http://www.postimage.org/image.php?v=Pq1PIcwr

[raysusan]

i love this thread

keep the qns coming and share

[Sarah]

[Moderator's note: Topics merged.]


Can anyone help?

Q1. Bobby, Edward and kelvin made a bottle of paper stars. The number of paper stars Bobby made was 21 more than 1/4 the total number of paper stars int he bottle. The num,ber of paper stars Edward made was 30 more than 1/4 of the remaining number of paper stars in the bottle. Kelvin made the remaining 114 paper stars. How many paper stars did they make in all?

Q2. A, B and C are three numbers. The average a, B and C is 5 greater tha the averaga of A and b. If C is 38, find the total of A, B and C.

Thank you.

[youngmum]

lizawa - i stil don’t understand still leh. So sorry. Got easier explanation?


How to do this?

May earned twice as much money as her brother. After May spent $32 and her brother spent $50, the ratio of money May had left to the amount of money her brother had left was 7:3. Find the amount of money May earned.

Thanks.

[corneyAmber]

youngmum, solution for new question as follows:


May ____________________________ ____________________________

May {---------32-------}{----------------------7 units-----------------------------------}

Bro ____________________________

Bro {------50-------------}{----3units----}

So the equation is:

32 + 7 units = 2(50 + 3 units)
32 + 7 units = 100 + 6 units
1 unit = 100-32 = 68

Hence May earned 7(68 )+32 = $508

[corneyAmber]

The other question is changing % into fractions that lizawa has cleverly done as it is easier to think in 1 unit than as 20% or 25%.

20% = 1 in 5 parts
25% = 1 in 4 parts

it is known total people = 1150
total non-photographers = 250
20% men and 25% women = 250 so in fraction:
1 unit of men + 1 unit of women = 250

since 1 unit of men and 1 unit of women are different things, it is hard to make comparison, however, we know that if we take away 4 units from men and women, the remainder is 1 unit of men.

hence 2504 = 1000
1150-1000 = 150
Only then you will know 1 unit of men(=20% of men) = 150

so total men(100% of men) = 1505 = 750

1 unit of women(=25% of women) = 250-150 = 100

so total women (100% of women) = 100*4 = 400

hence difference between men and women = 750-400=350

[ChiefKiasu]

Sarah:

...Q1. Bobby, Edward and kelvin made a bottle of paper stars. The number of paper stars Bobby made was 21 more than 1/4 the total number of paper stars in the bottle. The number of paper stars Edward made was 30 more than 1/4 of the remaining number of paper stars in the bottle. Kelvin made the remaining 114 paper stars. How many paper stars did they make in all?

Start backwards from Edward. Since Edward made 30 more than a quarter of the stars and Kelvin made the rest, it means that Kelvin's stars plus 30 makes up 3/4 of the stars,
ie. 114 + 30 = 144 is 3/4 of the stars
So the sum of Edward's and Kelvin's stars is 144 x 4/3 = 192

We apply the same principle with Bobby's stars now.
3/4 of the total stars = 192 + 21 = 213
So the total number of stars made by all 3 children is 213 x 4/3 = 284

Sarah:

...Q2. A, B and C are three numbers. The average of A, B and C is 5 greater than the average of A and B. If C is 38, find the total of A, B and C...

(A+B+C)/3 = (A+B)/2 + 5
A+B+C = 3(A+B)/2 + 15
A+B+38 = 3(A+B)/2 + 15
A+B+23 = 3(A+B)/2
2(A+B)+46 = 3(A+B)
=> A+B = 46
=> A+B+C = 46 + 38 = 84