Q&A - P5 Math

[MathIzzzFun]

ozora:

MathIzzzFun:

need some guide for the following questions.

1) ada and siti had some stamps in the ratio of 3:4.
after Ada bought 5 more stamps and siti gave away 1/5 of her stamps, they had the same number of stamps.
How many stamps did siti give away and what was the total number of stamps for 2 girls at first?



2)there were 1600 participants in a game. 30% were male participants.
when more male participants joined in, the male participants were increased to 60%. How many male participants joined in the contest?
is the answer : 1200 for this question?

1)
ada's stamps : siti stamps = 3 : 4 --> 15u : 20u
after giving away 1/5, siti's stamps left --> 4/5 x 20u = 16u
16u = 15u + 5, 1u --> 5
...I believe you can continue from here..

2)
at first, male --> 0.3 x 1600 = 480, female --> 1600-480=1120
in the end, male participants--> 60%, female participants--> 40%

no change in number of female participants, so 1120 = 40% of total number in the end

number of male participants in the end --> 1120/2 x 3= 1680
additional number of male participants who joined --> 1680-480=1200

cheers.

Thanks . Can solve q2 but unsure of the answer. As no answer key.
However for q1, is it due to common multiple of 4 n 5? Thus change 3:4 to 15:20?

For Q1, it is given that Siti gave away 1/5 of her stamps.. in the given ratio 3:4, Siti's share is not a multiple of 5. So, multiply by 5 to make calculation easier, otherwise will need to work with fractions.

cheers.

[terilyn]

Thank you very much

[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

[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.

[mathnoobs]

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

[MathIzzzFun]

mathnoobs:

MathIzzzFun:

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

is this an exam question ? could you post the original question?

cheers.

[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

[mathnoobs]

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 ?

[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\">

[MathIzzzFun]

mathnoobs:

tianzhu:

[quote=\"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 ?[/quote]\"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.