Q&A - P5 Math

[tianzhu]

concerned1970:

So sry i dun get u. Why did we have to get common multiple for 3 and 5?

Hi

I believe your child should have learned the “Equal concepts” from his school teacher.

In this question, one part of children is not the same as one part of children as each box in the MD is of different sizes as they represent different objects.

We want to make a comparison so we equalise the numerators of the two fractions 3/5 and 5/7.

3 and 5 have a common multiple of 15.

Please get your child to draw a model as it might help him/her to see better.

I am sorry, I don't have time to draw one now.

Best wishes

[mrswongtuition]

Something is wrong with the photo uploader here.


Anyway, the answer is here: https://www.facebook.com/media/set/?set=a.339535342767810.82445.118642878190392&type=1#!/photo.php?fbid=347705798617431&set=a.339535342767810.82445.118642878190392&type=3&theater

[concerned1970]

mrswongtuition:

Something is wrong with the photo uploader here.


Anyway, the answer is here: https://www.facebook.com/media/set/?set=a.339535342767810.82445.118642878190392&type=1#!/photo.php?fbid=347705798617431&set=a.339535342767810.82445.118642878190392&type=3&theater

Ty so much Mrs Wong for yr MD.

[concerned1970]

No Pb, Tianzhu. U've helped me alot.

[ozora]

MathIzzzFun:

ozora:

need some guide in this question. Tank A and Tank B are identical. Tank A is 2/5 full of water while tank B is 6/7 full of water. The mass of Tank A with its contents is 7/10 of The mass of Tank B with its contents. The total mass of the 2 tanks and their contents is 374kg. Find the mass of an empty tank.

Hi

mass of tank A with contents --> 7/17 x 374 kg = 154 kg
mass of tank B with contents --> 374 kg - 154 kg = 220 kg
(6/7-2/5)tank of water --> 220 - 154 = 66 kg
16/35 tank of water --> 66 kg
mass of tank = 220 - 6/7 tank of water = 220 - 30/16 x 66 = 96.25 kg
(** 6/7 tank of water = 30/35 tank of water = 30/16 x 66 kg)

most schools are teaching/doing ratio sums at the moment, here's alternate approach using ratio:
difference in mass of tanks with contents = difference in mass of contents
mass of water in tank A : tank B = 2/5 : 6/7 = 7 : 15
mass of tank A with contents : tank B with contents = 7 : 10
\"equalize\" the difference:
mass of water in tank A : tank B = 21u : 45u
mass of tank A with contents : tank B with contents = 56u : 80u
mass of tank = 56u - 21u = 80u-45u = 35u
total mass of both tanks with contents = 136u
mass of tank = 35/136 x 374 = 96.25 kg


cheers.

thanks
i did a different method which is using
16/35->66
1/35->4/125
2/5-> 14/35
12/35-> 57.75

154-57.75=96.25kg

thanks again for confirming my answer.

[sunnydays2]

Hi, I’ve got 2 Math questions.


1. Alan and Dennis had some money. If Alan spends $70 and Dennis spends $35, Alan will have $515 left. If Alan spends $35 and Dennis spends $70, Alan will have $2300 left. How much does each of them have?

2. Mr Lim had some stickers and stamps for his class. The number of stickers was 1/2 the number of stamps. After each pupil in the class had received 3 stickers and 8 stamps from Mr Lim, he had 39 stickers and 2 stamps left. What was the total number of stickers and stamps Mr Lim had at first?

[speedmaths.012624com]

sunnydays2:

Hi, I've got 2 Math questions.


1. Alan and Dennis had some money. If Alan spends $70 and Dennis spends $35, Alan will have $515 left. If Alan spends $35 and Dennis spends $70, Alan will have $2300 left. How much does each of them have?

Hi,

Question 1 looks incomplete.
(Probably needs to add \"when Dennis has spent all his money\".)

Anyway, for such questions, one solution is to look at the ratios rather than the actual numbers.

Look at the example given in Chapter 1 of the Raffles Maths Tricks Volume 1 book (see below):

http://i50.tinypic.com/2m7aoev.jpg\">

Can you use the example given above to solve Question 1?

Cheers

speedmaths.com

-

[tianzhu]

sunnydays2:

2. Mr Lim had some stickers and stamps for his class. The number of stickers was 1/2 the number of stamps. After each pupil in the class had received 3 stickers and 8 stamps from Mr Lim, he had 39 stickers and 2 stamps left. What was the total number of stickers and stamps Mr Lim had at first?

Hi

Hope this helps.

Best wishes

http://farm8.staticflickr.com/7214/6994422784_250a9bcd20_z.jpg\">

[prayhardmum]

Can someone help the following question, please? Thanks.


Three sisters Lisa, Ming and Nora shared the cost of a present to their father. Lisa paid 1/4 of the total share of Ming and Nora. Ming paid 1/9 of the total share of Lisa and Nora. Nora paid $60 more than Ming. How much did the present cost?

[mrswongtuition]

prayhardmum:

Can someone help the following question, please? Thanks.


Three sisters Lisa, Ming and Nora shared the cost of a present to their father. Lisa paid 1/4 of the total share of Ming and Nora. Ming paid 1/9 of the total share of Lisa and Nora. Nora paid $60 more than Ming. How much did the present cost?

L : N : M : Total
1: -- 4 --: 5
-- 9--: 1 : 10

The total amount is the same.
Therefore we need to multiply the first ratio by 2 to make the total number of units the same.

L : N : M : Total
2: -- 8 --: 10
-- 9--: 1 : 10
2 : 7 : 1 : 10

7 - 1 = 6 units
6 u --> $60
1 u --> $10
10 u --> $100