## Q&A - PSLE Math

- Whitearies
- GreenBelt
**Posts:**115**Joined:**Thu Aug 01,

### Re: Q&A - PSLE Math

Mr Koh had red, blue and yellow roses for sale in his nursery. There were 60 more pots of blue roses than yellow roses. He had 10 more pots of red roses than blue roses. After selling 3/4 of the pots of blue roses and 1/2 of the pots of yellow roses, there were 358 pots of roses left. How many pots of red roses did Mr Koh have at first?

- Whitearies
- GreenBelt
**Posts:**115**Joined:**Thu Aug 01,

### Re: Q&A - PSLE Math

The teachers in ABC Primary School are divided equally into 3 groups, X, Y and Z. The number of male teachers in Group X is equal to the number of female teachers in a Group Y. 1/4 of the school male teachers are in Group Z.

a) Find the ratio of the number of male teachers to the number of female teachers in the school.

b) If there are 45 female teachers in Group X and Y, how many male teachers are there in the school?

a) Find the ratio of the number of male teachers to the number of female teachers in the school.

b) If there are 45 female teachers in Group X and Y, how many male teachers are there in the school?

### Re: Q&A - PSLE Math

a) Delta between one correct and one wrong answer is 6+4 = 10 pointsSruthi wrote: please help me with this question

Assume all questions are correct, = 20 X6 = 120points

Actual score =0

Number of wrong question = (120-0)/10 =12 questions

therefore he answered 20-12 = 8 questions correctly.

b) If the number of correct and incorrect question is the same, we can denote the number of questions they both share with a same variable. Let the number of questions answered either correctly or incorrectly be Q

6Q - 4Q =16

2Q=16

Q=8

Therefore he answered 8 questions correctly and 8 questions incorrectly.

Number of quesiton he left blank = 20 - 8 - 8 = 4

### Re: Q&A - PSLE Math

Hope someone has a simpler solution, mine is here,Whitearies wrote:The teachers in ABC Primary School are divided equally into 3 groups, X, Y and Z. The number of male teachers in Group X is equal to the number of female teachers in a Group Y. 1/4 of the school male teachers are in Group Z.

a) Find the ratio of the number of male teachers to the number of female teachers in the school.

b) If there are 45 female teachers in Group X and Y, how many male teachers are there in the school?

http://www.kiasuparents.com/kiasu/forum ... 6#p1447976

### Re: Q&A - PSLE Math

Blue and red can be reference to Yellow. Let Yellow be 4yWhitearies wrote:Mr Koh had red, blue and yellow roses for sale in his nursery. There were 60 more pots of blue roses than yellow roses. He had 10 more pots of red roses than blue roses. After selling 3/4 of the pots of blue roses and 1/2 of the pots of yellow roses, there were 358 pots of roses left. How many pots of red roses did Mr Koh have at first?

Yellow = 4y

Blue =4y+60

Red = 4y+70

After selling 1/2 of yellow and 1/4 of blue,

Yellow =2y

Blue = y+15

Red = 4y+70

Altogether left, 2y+y+15+4y+70 = 358

7y=273

y=39

Red = 4y+70 = 4(39)+70=226

### Re: Q&A - PSLE Math

Looking at several possible before and after ratio, finally selected these pair of ratio that have common units.Whitearies wrote:Denise and Eddy shared a number of markers in the ratio 5:6. After Denise bought another 14 markers and Eddy gave away 4 markers, the ratio become 8:7. How many markers did Denise have in the end?

Before D:E = >25u:30u

After D:E => 32u:28u

Reasons for selecting the above pair of ratio is D increase by 7u and E decrease by 2u. 7u is 3.5 times of 2u. This matches the absolute value of 14 markers bought and 4 markers given, also 3.5 times. Base on this condition the selected pair of ratio above have common units.

7u=14

u=2

in the end D has 32u=32(2)=64 markers

### Re: Q&A - PSLE Math

Another method to try (which I find easier for me to understand):Ender wrote:Looking at several possible before and after ratio, finally selected these pair of ratio that have common units.Whitearies wrote:Denise and Eddy shared a number of markers in the ratio 5:6. After Denise bought another 14 markers and Eddy gave away 4 markers, the ratio become 8:7. How many markers did Denise have in the end?

Before D:E = >25u:30u

After D:E => 32u:28u

Reasons for selecting the above pair of ratio is D increase by 7u and E decrease by 2u. 7u is 3.5 times of 2u. This matches the absolute value of 14 markers bought and 4 markers given, also 3.5 times. Base on this condition the selected pair of ratio above have common units.

7u=14

u=2

in the end D has 32u=32(2)=64 markers

D : E

At first 5u : 6u

Changes +14 : -4

After 8p : 7p

As there are changes in D,E,T (Dennis, Eddy, Total), will make the "u" to be the same at first. Common factor of 5u and 6u will be 30.

Multiply by common factor of 5 & 6.

D x6 : E x 5

At first 30u : 30u

Changes +84 : -20

After 48p : 35p

Therefore, (48p-35p) = 13p

13p = 84+20 = 104

1p = 8

8p (Original for Denis (8p) before multiply by 6) = 8 x 8 = 64

### Re: Q&A - PSLE Math

Alternate Method:Sruthi wrote: please let me know if thd working done is correct.is there any other alternative methods we can use to solve this problem

**At First**:

Let

Total salary = 100 units

Mr. Lin saves 30% of his salary

**At first Savings = 30/100*100 units = 30 units**

**After Rise in Salary**:

10% rise in salary means,

Total salary = 100 units + 10/100*100 units = 110 units

Mr. Lin still saves 30% of his new salary

**In the end Savings = 30/100*110 units = 33 units**

**Difference in savings**= 33 units - 30 units = 3 units.

It is given that,

Increase in savings after salary raise = $189

Therefore 3 units = $189

**1 unit = $189/3 = $63**

Salary at first = 100 units

**Actual Salary = 100 * $63 = $6300**

### Re: Q&A - PSLE Math

I agree, your method is easier to understand. I will use your method to teach my son instead. It looks very similar to the simultaneous equation I would use.lynntan15 wrote: Another method to try (which I find easier for me to understand):

D : E

At first 5u : 6u

Changes +14 : -4

After 8p : 7p

As there are changes in D,E,T (Dennis, Eddy, Total), will make the "u" to be the same at first. Common factor of 5u and 6u will be 30.

Multiply by common factor of 5 & 6.

D x6 : E x 5

At first 30u : 30u

Changes +84 : -20

After 48p : 35p

Therefore, (48p-35p) = 13p

13p = 84+20 = 104

1p = 8

8p (Original for Denis (8p) before multiply by 6) = 8 x 8 = 64

5u+14 =8p => 30u+84=48p ----(1)

6u-14 =7p => 30u-20=35p ----(2)

(1)-(2)

84+20 =13p

p=8

finally D has 8p=64

Last edited by Ender on Tue Feb 24, 2015 10:21 am, edited 1 time in total.

### Re: Q&A - PSLE Math

You might also want to explain why is it 8p and not 48p.Ender wrote: I agree, your method is easier to understand. I will use your method to teach my son instead.

Becoz if you imagine it to be "model", you are taking the whole "block" to multiply and not cut the model into smaller piece. As such, you have to take the original "p".

HTH.