Q&A - P5 Math

[PapayaDad]

Assume 21 man and 21 woman. Total 42


2/7 men = 6
1/3 woment = 7
Total alighted = 13
So 29 did not alight. Answer 29/42

[chloecube]

PapayaDad:

Assume 21 man and 21 woman. Total 42


2/7 men = 6
1/3 woment = 7
Total alighted = 13
So 29 did not alight. Answer 29/42

thks papayaDad

i do not quite understand, what i did was
i change the denominator to the same,
2/7 - 6/21
1/3 - 7/21
total of alighted pax = 13/21
so 8/21 did not alight

something wrong with my method?

[MathIzzzFun]

chloecube:

PapayaDad:

Assume 21 man and 21 woman. Total 42


2/7 men = 6
1/3 woment = 7
Total alighted = 13
So 29 did not alight. Answer 29/42

thks papayaDad

i do not quite understand, what i did was
i change the denominator to the same,
2/7 - 6/21
1/3 - 7/21
total of alighted pax = 13/21
so 8/21 did not alight

something wrong with my method?

total alighted should be 13/42
because there are equal number of men and women, so the total number of people is doubled ie 21 + 21 = 42.

29/42 did not alight

cheers.

[chloecube]

thks papayadad

[veraclari]

Hi all thanks to the sharing s here I know ratio must use cross multiply method sometimes. However can u kindly share how we determine what to cross multiply or the factor to multiply as I’m confused…Eg. In the qquestion and model answer attached, why X 6 & X 7? How to dderive 6&7? TIA!


Qn: ratio of no. Of girl to boy is 6:5. No. Of girl swimmers to girl non swimmers is 5:2. Ratio of boy swimmers to boy non swimmers is 3:2.
A) what fraction of children is non swimmers?
B) if there were 30 more boys non swimmers than girl non swimmers. How many swimmers were there altogether?
Model Answer

‘’‘’‘’‘’ 5 : 2 ---------3 : 2
((X6)) 30 : 12 ---------21 : 14 ((X7))
A) total units -> 42+35= 77
Total non swimmers -> 12+14 = 26

Kindly advise why they multiply by 6&7? How to get 6&7 in e first place?

Thanks! !!
P.s.I am new to this and am using mobile upload and I can’t rotate e picture which is turned when uploaded though original is upright Sso I didn’t Upload. How to rotate in tinypic?

[Jamesbond]

MathIzzzFun:

Jamesbond:

A box contained a number of 20 cent and 50 cent coins in the ratio 3:4. When ten 50 cent coins were taken out and replaced by 20 cent coins, the ratio became 7:5. Find the sum of money in the box at first?

Pl help.

possible approaches - cross-multiply/UP, units, MD.

Using units:

10 x $0.50 = 25 x $0.20
--> 10 fifty-cent coins were replaced by 25 twenty-cent coins

At first
number of 50c --> 20 units + 10
number of 20c (= 3/4 number of 50c) --> 15 units + 7.5

In the end,
number of 50c --> 20 units
number of 20c (=7/5 number of 50c) --> 28 units

since 25 twenty-cent coins were added, we have:

15 units + 7.5 + 25 = 28 units
1 unit --> 2.5

Sum of money in the box at first
= sum of money in the box in the end
= 20 x 2.5 x $0.50 + 28 x 2.5 x $0.20
= $39

cheers.

Thank you MathIzzzFun for your help. Why this sum has to be soo difficult? I managed to understand.

[Jamesbond]

In a classroom, when 5 boys left for the washroom, the ratio of the number of boys to the number of girls that remained became 1:1. On the other hand, when 5 girls left the classroom, the ratio of the number of boys to the number of girls that remained became 5:3. How many boys and girls were there in the class? :?

[jieheng]

Jamesbond:

In a classroom, when 5 boys left for the washroom, the ratio of the number of boys to the number of girls that remained became 1:1. On the other hand, when 5 girls left the classroom, the ratio of the number of boys to the number of girls that remained became 5:3. How many boys and girls were there in the class? :?

In a classroom
B [----------][5]
G [----------]

B [--3u--][5][5]
G [--3u--][5]

5u --> 3u + 5 + 5
2u --> 10
1u --> 5

No. of boys = 3u + 5 + 5 = 3*5 + 10 = 25

No. of girls = 3u + 5 = 3*5 + 5 = 20

[heyhoe]

Hi,


My DS needs help with Maths questions. Appreciate your assistance.

1st
There were 3/5 as many adults as children on a bus. At the next stop, 6 adults and 4 children boarded the bus. As a result, there were 3/4 as much adults as children on the bus. How many people were on the bus then?

Thanks

[jieheng]

heyhoe:

Hi,


My DS needs help with Maths questions. Appreciate your assistance.

1st
There were 3/5 as many adults as children on a bus. At the next stop, 6 adults and 4 children boarded the bus. As a result, there were 3/4 as much adults as children on the bus. How many people were on the bus then?

Thanks

At first
A [][][]
C [][][][][]

At the next stop
A [][][] + 6 -------------- 3x
C [][][][][] + 4 ---------- 4x

3x --> [][][] + 6
1x --> [] + 2
4x --> [][][][] + 8

[][][][][] + 4 --> [][][][] + 8
[] --> 4

No of people were on the bus then = ([][][] + 6) + ([][][][][] + 4) = 42