Q&A - P5 Math

[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.

[mathnoobs]

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.

[mathnoobs]

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:

[ftwm]

Molly had some flour. She used an equal amount of flour daily to bake cakes. After 15 days, she had 3/8 of the flour left. After another 3 days, she had 3 3/4 of flour left. How much flour did she use in 12 days?


pls assist. tq.

[ftwm]

hi need help in this Q.


1/5 of a rectangular tank measuring 30cm long, 20cm wide and 10cm high was filled with water. The ratio of the volume of the water in the tank to that in a bottle was 4 : 3. When some water was poured out of the bottle into the tank, the ratio of the new volume of water in the tank to that in the bottle was 2 : 1. How much water had been poured out of the bottle?

Tq.

[bookwormkids]

Question:

Oscar and Mavis have some beads. If Oscar gives Mavis 30 beads, he will have twice as many beads as Mavis. If Mavis gives Oscar 30 beads, the ratio of the number of beads she has to the number of beads Oscar has will be 1 : 5. How many beads doe each of them have at first?

Thanks.

[tianzhu]

ftwm:

Molly had some flour. She used an equal amount of flour daily to bake cakes. After 15 days, she had 3/8 of the flour left. After another 3 days, she had 3 3/4 of flour left. How much flour did she use in 12 days?


pls assist. tq.

Hi

You may use MD, units or work with fractions.

15 days ------- 5 units of the flour

3 days ------- 1 unit of the flour

18 days ------- 6 units of the flour

Total amount of flour ------- 8 units

2 units ------- 15/4 of the flour

12 days -------- 4 units ------- 15/4*2 ------ 7½ of the flour.

You may also use fractions.

15 days ------- 5/8

3 days ------ 1/8

18 days ------- 6/8 -------3/4

1/4 --------- 15/4

4/4 ------- 15

24 days ------ 15

12 days ------- ½ of 15 ------ 7½

Best wishes

[tianzhu]

ftwm:

hi need help in this Q.


1/5 of a rectangular tank measuring 30cm long, 20cm wide and 10cm high was filled with water. The ratio of the volume of the water in the tank to that in a bottle was 4 : 3. When some water was poured out of the bottle into the tank, the ratio of the new volume of water in the tank to that in the bottle was 2 : 1. How much water had been poured out of the bottle?

Tq.

Hi

Amount of water in rectangular tank ------- 30*20*10*1/5 ------1200

At first

Tank ----- 4 units ------- 1200

Bottle ------ 3 units ------ 900

The amount of water remains the same before and after (2100).

In the end

Tank ----- 1400 (2)

Bottle ------ 700 (1)

Volume of water from bottle to tank ------- 200

Best wishes