tianzhu:

mathnoobs:

For the P6 version, I too was of the opinion that something was not quite right. To have a question that has multiple answers is unfair, especially under exam conditions. At the very least, they should have constrained the answer to a single value by giving some additional conditions.

Hi

If a question is crafted correctly, there should be only one correct answer.
If not, there is a possibility of multiple answers.

Ideally it should not happen, but realistically it is an inescapable fact of life that we are living in an imperfect world.

These are some examples of questions discussed in this forum which have multiple answers.

1) Dean,Ellen and Andy shared a box of sweets in the ratio of 3:4:5 and there was 4 left .They put the 4 sweets into a second box which contained 1/8 fewer sweets than the first box, and shared the sweets in the same ratio as before,and this time there were no remainder.
A)Find the total number of sweets they shared in the first round.
B)Find the total number of sweets each child received in both rounds of sharing.

2) Jenny bought some strawberries and wanted to put them into boxes. If she put 4 strawberries into each box, there will be 3 strawberries left. If she put 6 strawberries into each box, there will be 5 strawberries left.
(a) If the nos. of strawberries is btw 100 - 150, how many strawberries did Jenny buy?
(b) If Jenny decided to put all strawberries equally into 16 bags, what is the minimum nos. of bag she would need?

Best wishes

thanks for the questions. think I'll need some time to work on the 1st question. The 2nd question seems more reasonable, at least they put in conditions by saying the range (100 - 150) and in (b) it is the minimum number. With these conditions, there should be only 1 correct answer for both (a) and (b).

yes, I do understand what you're saying. Life is tough, it is unfair. The positive note to that is that it works both ways. ie. pupils who are not academically inclined can also succeed in life. Not everyone who succeeds have to score A* in the exams. Adam Khoo is a good example. Richard Branson is another.

first, I must clarify that my query was on the P6 version, not the P5 version. I fully comprehend the P5 version, that makes sense.

For the P6 version, I too was of the opinion that something was not quite right. To have a question that has multiple answers is unfair, especially under exam conditions. At the very least, they should have constrained the answer to a single value by giving some additional conditions.

anyways, thanks Tianzhu and MathIzzFun for clearing my doubts. I was on the track that there was only one possible solution, and could not comprehend why 15% = 38.25. Now I know that 15% could represent a number of possible values, not just 38.25. Actually, the condition is based on the difference between the discounted price, and there are infinite values that satisfy that condition.

actually, I just realized that the student can write any numerical answer and it will still be right. Am I right to say this ?
if this is so , then all students would have scored in this question, because there are no wrong answers for this question. This would be a 'gift' question then. hey, I do like this question after all

wait, no, not any values, just any values greater than 38.25.

tianzhu:

Robertpattinsonidle:

this question seriously mind boggling.



Both shops ABC and XYZ , offered a 15% discount for the same type of mattress. If Mr Muthu were to buy from shop XYZ ,he would have paid $38.25 less than the discounted price in shop ABC. a) What was the discounted price in the shop ABC ?
b) the original price of the mattress in Shop ABC was $1510. what was the minimum percentage discount it must offer so that the discounted price in shop ABC would be lower than the discounted price in Shop XYZ? Give your answer correct to the nearest percent.

Hi
This question has been discussed on page 837.

For (a)

15% ------- 38.25

100% ------- 255 (discounted price in ABC)

For (b)

In this case, we are working based on the given original price of $1510

Discounted price in ABC -------- 1510*0.85 ------ 1283.50

Discounted price in XYZ -------- 1283.50 – 38.25 ------- 1245.25

1510 – 1425.25 ------- 264.75

264.75/1510*100% ------- 18%

Best wishes

I've been pondering about this question, but I just can't understand this statement:
15% ------- 38.25

100% ------- 255 (discounted price in ABC)

the question states that the difference between XYZ and ABC's discounted price is $38.25.
The discount given by both shops were 15% each. How does one interpret that 15% = 38.25 ?

tianzhu:

mathnoobs:

The problem I have though is:
10u - 4 = 9u

I don't see how the 4 fits in there.
What does 3/5 of girls + 4 girls mean ?

Hi

Based on the given answer of 100 pupils, we can say that the number of girls added to the class is 4.The number of boys being replaced is also 4.

Best wishes

http://farm9.staticflickr.com/8311/8028173647_e8bac2a7f9_z.jpg\">

thank you for the detail graphics Tianzhu. :thankyou:

MathIzzzFun:

\"In the end, boys is 3/5 of girls + 4 girls\" could mean :
1) there are 4 more girls in the end, and the number of boys is 3/5 the number of girls --> in this case, the answer is 160 pupils

2) the number of boys is 4 more than 3/5 the number of girls --> in the case, there are multiple answers, the minimum number of pupils is 140

3) the number of boys is 3/5 the original number of girls and there are 4 more girls in the end --> solution as in tianzhu post

cheers.

thank you for your explanation, MathIzzfun. It makes sense now.

tianzhu:

mathnoobs:

this question looks like an Unchanged Total problem to me. But I'm stumped by the +4 girls.


In a class, the number of boys left was replaced by the same number of girls. At first boys is 2/3 of girls. In the end, boys is 3/5 of girls + 4 girls. Find the number of pupils in the class at first ? Ans: 100 pupils

Hi

Where is this question from?

At first boys is 2/3 of girls.

Boys:Girls ------- 2:3 ------ 10:15

The number of boys left was replaced by the same number of girls. In the end, boys is 3/5 of girls + 4 girls.

Boys:Girls ------- 3:5 + 4 girls -------9:15 + 4 girls

10 u – 4 ------- 9u

1u ------- 4

Number of pupils@first ------- 25*4 ------- 100

Best wishes

it's a problem that came from a friend, so I don't know it's origins. It is the full question, I've not edited it in anyway.

The problem I have though is:
10u - 4 = 9u

I don't see how the 4 fits in there.
What does 3/5 of girls + 4 girls mean ?

MathIzzzFun:

mathnoobs:

this question looks like an Unchanged Total problem to me. But I'm stumped by the +4 girls.


In a class, the number of boys left was replaced by the same number of girls. At first boys is 2/3 of girls. In the end, boys is 3/5 of girls + 4 girls. Find the number of pupils in the class at first ? Ans: 100 pupils

I interpret the question as:

In a class, the number of boys who left the class was replaced by same number of girls. At first, the number of boys was 2/3 the number of girls. In the end, the number of boys is 4 more than 3/5 the number of girls. Find the number of pupils in the class at first ?

is this correct ? If it is, there are multiple answers and the minimum number of pupils = 140. If there are 100 pupils the number of girls at first is equal to the number of girls in the end, which is incorrect.

cheers.

I'm not sure if your interpretation is correct since I'm confused with the interpretation myself. However, the model answer seems wrong.

The model answer was:
At first: Boy: Girl -> 2:3
At End: Boy: Girl -> 3:5 + 4 girls
At First: 2/3 x 5x5 = 10/15
At End: (3/5 + 4 girls ) x 3/3 = 9/15 + 4 girls
10 units = 9 units + 4 girls
1 unit = 4 girls/pupil
Total Pupils = (10 units + 15 units) x 4 pupils = 100

this question looks like an Unchanged Total problem to me. But I’m stumped by the +4 girls.


In a class, the number of boys left was replaced by the same number of girls. At first boys is 2/3 of girls. In the end, boys is 3/5 of girls + 4 girls. Find the number of pupils in the class at first ? Ans: 100 pupils

MathIzzzFun:

pineapple tarts:

Hi again,


This one look so simple but I can't get the correct anwser. Hope u can help.

Mrs Tan has more than 120 cookies. If she put them into packets of 7, she has 5 cookies left. If she puts them in packet if 9, she has 1 cookie left. What is the least nos. of cookies Mrs Tan has?

Thank you.

One approach --> listing, with a slight twist:

7 & 9 --> lowest common multiple = 63
Possible number will lie between 63 & 126

List multiple of 9 and add 1,
we get: 64, 73, 82, 91, 100, 109, 118
divide by 7, find remainder (in bracket)
--> 64 (1), 73 (3), 82 (5), 91 (0), 100 (2), 109 (4), 118 (6)

Look for remainder of 5 --> 82

Mrs Tan had 82 cookies.

cheers.

I don't quite understand this.
Mrs Tan should have more than 120 cookies.
Based on this criteria, the next number in line after 82, with a remainder of 5 should be 145. Or am I wrong in this ? :?

tianzhu:

mathnoobs:

Hi Tianzhu

I'm afraid I'm a bit weak in geometry. Hard to visualize things.
I can see the area of a quadrant, which is 1/4 of area of circle, radius 7cm. I can also see the area of isosceles triangle, which is 1/2 area of square.
But I don't see how (area of quadrant - area of triangle)/2 leads to difference in the 2 shaded regions.

Hi

You're on the right track as you can see the quadrant and isosceles triangle.

I'll prepare the sketch to show you how (area of quadrant - area of triangle)/2 leads to difference in the 2 shaded regions.

Watch your PM.Please give me some time.

Best wishes

Hi Tianzhu
thank you for your offer to help. I appreciate it very much.
No hurry. I've plenty of maths problems to work on in the meantime.
Happy Easter.