Q&A - P5 Math

[tianzhu]

Shimmer:

Hi

2. There were 240 people in a shopping centre. 3/5 of them were men. Some men then left the shopping centre. The number of men in the shopping centre was 4/7 of the remaining people. How many men left the shopping centre ?

Hi

At first
men:women ------ 3:2 ------- (x3) ------- 9:6

In the end
men:women ------ 4:3 -------- (x2) ------- 8:6

The number of women before and after stays the same, so make the units for women the same.

15 units ------ 240

1 unit ------ 16

Number of men@left shopping centre ------16

Best wishes

[hazelwong]

Hi, can anyone help with this qn?

Mrs tan bought 42 apples. Each apple costs 75cents less than a pear. She spent the same amount of money on 12 pears. How much did Mrs Tan spend on buying the apples?

I managed to solve it only with algebra:
let X be price of pear
42 (X-0.75) = 12X
42X-31.50 = 12X
30X = 31.50
X = 1.05
price of apple 1.05- 0.75 = 0.3
42x0.3 = 12.60
Ans $12.60

Is using algebra ok?
Is there any other way e.g. model or units/parts?
thanks v much

[MathIzzzFun]

hazelwong:

Hi, can anyone help with this qn?

Mrs tan bought 42 apples. Each apple costs 75cents less than a pear. She spent the same amount of money on 12 pears. How much did Mrs Tan spend on buying the apples?

I managed to solve it only with algebra:
let X be price of pear
42 (X-0.75) = 12X
42X-31.50 = 12X
30X = 31.50
X = 1.05
price of apple 1.05- 0.75 = 0.3
42x0.3 = 12.60
Ans $12.60

Is using algebra ok?
Is there any other way e.g. model or units/parts?
thanks v much

cost of 42 apples = cost of 12 pears
cost of 1 apple = 12/42 cost of 1 pear = 2/7 cost of 1 pear
1 pear --> 7 units
1 apple --> 2 units

1 apple cost 75 cents less than 1 pear,
5 units --> 75 cents
1 unit --> 15 cents

cost of 1 apple --> 30 cents
cost of 42 apples --> 42 x $0.30 = $ 12.60

cheers.

[chloecube]

carol73:

hi


how do you determine that now is 3units
thanks

chloecube:

[quote=\"carol73\"]The Queen, prince and princess had 270 diamonds. After receiving 90 diamonds for her birthday, the Queen decided to give 1/2 of the diamonds to the prince, the prince than gave 2/5 of his diamonds to the princess.in the end the three of them had the same number of diamonds, how many diamonds did each of them have at first

270 + 90 = 360

now -
Queen - 3 units
Prince - 3 units
princess - 3 units

work backwards
before -
Queen - 6 units
Prince - 2 units
princess - 1 unit

9u - 360
1u - 40

so Queen - 240 - 90 = 150
Prince - 80
princess - 40

[/quote]hi,
i work backwards, starting with the Prince, he gave 2/5 to the princess, so he left 3units. and in the end they all have the same nos of unit.
so i take it as all of them have 3 units and i work slowly from there

[purple05]

All 150 seats at the back row of a concert hall are priced at 3/5 that of the other seats. There are 600 seats altogether, and when all the seats are sold, the amount collected is $2700. Find the price of each seat at the back row of the concert hall

[PapayaDad]

150 x 3/5 = 90


Number of other seats = 600-150=450

450+90=540

2700/540=5 (price of other seat)

back row = 3

check
450x5=2250
150x3= 450
Total = 2700…correct

[MathIzzzFun]

purple05:

All 150 seats at the back row of a concert hall are priced at 3/5 that of the other seats. There are 600 seats altogether, and when all the seats are sold, the amount collected is $2700. Find the price of each seat at the back row of the concert hall

using units approach...

price of normal seat --> 5 units
price of back row seat --> 3 units

Total collected --> (600-150) x 5 units + 150 x 3 units = 2700 units
2700 units --> $ 2700
1 unit --> $1

Price of normal seat --> $5
price of back row seat --> $3

cheers.

[chloecube]

hi, need help for the followings:


classes 5A and 5B have the same number of pupils. the ratio of the number of boys in 5A to the number of boys in 5B is 2:3. the ratio of the number of girls in 5A to the number of girls in 5B is 7:4.
a) find the ratio of the number of boys to the number of girls in 5A.
b) if there are 15 fewer girls than boys in 5B, how many pupils are there in 5B?

container A and container B are identical. container A is 3/3 filled with water while container B is 1/3 filled with water. the ratio of the total mass of container A and its contents to the total mass of container B and its contents is 7:5. the total mass of 2 containers with their contents is 1020g. what is the mass of each empty container?

[MathIzzzFun]

chloecube:

hi, need help for the followings:


classes 5A and 5B have the same number of pupils. the ratio of the number of boys in 5A to the number of boys in 5B is 2:3. the ratio of the number of girls in 5A to the number of girls in 5B is 7:4.
a) find the ratio of the number of boys to the number of girls in 5A.
b) if there are 15 fewer girls than boys in 5B, how many pupils are there in 5B?

solution using MD --> http://www.flickr.com/photos/mathizzzfun/5760364658/in/photostream


Since the number of pupils in both classes is the same, the difference of the ratio parts for girls and boys must be the same

boys in 5A : boys in 5B = 2 : 3 --> difference of 1
girls in 5A : girls in 5B 7 : 4 --> difference of 3

make the difference the same :

boys in 5A : boys in 5B --> 6u : 9u ---- difference of 3u
girls in 5A : girls in 5B --- 7u : 4u ----- difference of 3u
Total number of pupils in each class --> 13u

In 5A, ratio of boys : girls = 6 : 7

15 fewer girls than boys in 5B
9u - 4u = 5u
5u --> 15, 1u --> 3

13 x 3 = 39

there are 39 pupils in 5B

cheers.

[MathIzzzFun]

chloecube:

hi, need help for the followings:



container A and container B are identical. container A is 2/3 filled with water while container B is 1/3 filled with water. the ratio of the total mass of container A and its contents to the total mass of container B and its contents is 7:5. the total mass of 2 containers with their contents is 1020g. what is the mass of each empty container?

I think there is a typo error ... 3/3 should be 2/3 ?

one key strategy to use when solving problem sum is --> 'divide and conquer\" .... break up the question into sub-question and find answer to each part first.

I have added a sub-question .. hopefully this help you solve the sum..

container A and container B are identical. container A is 2/3 filled with water while container B is 1/3 filled with water. the ratio of the total mass of container A and its contents to the total mass of container B and its contents is 7:5. the total mass of 2 containers with their contents is 1020g.

a) what is the mass of each container with its contents ?
b) what is the mass of each empty container?

cheers.