Q&A - P5 Math

[andyle.024255sg]

chloecube:

school teacher method look complex to me, any one can help with model or perhaps other simpler method for this sum?


Muna and Rita had 360 seashell. Muna gave 4/7 of her seashells to Rita. in return, rita gave 2/5 of her total number of seashells to Muna. then they have an equal number of seashells each. how many seashells did each of them have at first?

How about working backwards?
At the end each have 180

After Rita gave 2/5, she had left 3/5, right?
3/5 of Rita -> 180
1/5 of Rita -> 60
5/5 of Rita -> 300
At that time, Muna had 60 (sum is 360)

Muna gave 4/7, hence she had left 3/7 (this is 60ss)
3/7 of Muna -> 60
7/7 of Muna -> 140
So at the beginning, Muna had 140
Rita had 360-140=220

Check:
Muna and Rita
Beginning: 140 and 220
After Muna gave 4/7 (80ss): 60 and 300
After Rita gave 2/5 (120ss): 180 and 180

Maybe drawing model better?

[doraemo]

The Right Equation:

carol73:

hi

pls help

1) Jamie spent $6 less than 4/7 of her money on a dress. She spent $6 more than 1/2 of ther remaining amount of money on a blouse. If she had $24left, how much money did she have at first

this qn uses drop-down model + working backwards. http://i40.tinypic.com/2ceqnm9.jpg\">

[/quote]

Hi The Right Equation
Would like to seek your clarification/explanation of the rationale behind in drawing the models in this manner.

[chloecube]

andyle.sg:

chloecube:

school teacher method look complex to me, any one can help with model or perhaps other simpler method for this sum?


Muna and Rita had 360 seashell. Muna gave 4/7 of her seashells to Rita. in return, rita gave 2/5 of her total number of seashells to Muna. then they have an equal number of seashells each. how many seashells did each of them have at first?

How about working backwards?
At the end each have 180

After Rita gave 2/5, she had left 3/5, right?
3/5 of Rita -> 180
1/5 of Rita -> 60
5/5 of Rita -> 300
At that time, Muna had 60 (sum is 360)

Muna gave 4/7, hence she had left 3/7 (this is 60ss)
3/7 of Muna -> 60
7/7 of Muna -> 140
So at the beginning, Muna had 140
Rita had 360-140=220

Check:
Muna and Rita
Beginning: 140 and 220
After Muna gave 4/7 (80ss): 60 and 300
After Rita gave 2/5 (120ss): 180 and 180

Maybe drawing model better?

so much clearer now
:thankyou:

[Awonder]

Oldschool:

Awonder:

There were a total of 930 boys and girls at a carnival. After 4/5 of the boys and 3/4 of the girls left, there were 120 more girls than boys that remained. How many girls were there at the carnival at first?

Hi,

http://i41.tinypic.com/1819ix.jpg\">

Regards

Thank you for the answer and Tianzhu too.

[veraclari]

Hi all, need help as I don’t understand why a method or step is done.

Julian has 5/7 as many marbles as Kenneth. Kenneth has 2/3 as many marbles as Alex. If Alex has 105 more marbles than Kenneth, how mamy more marbles than Julian does Alex Have?

Solution step 1:
5/7 = 10/14 ( convert by multiplying by 2)

2/3 = 14/21 (convert by multiplying by 7)

I know they do the above to find difference in units between Kenneth and Alex. BUT how do we Detemine or Know that must be Multiplied by X 2 & X 7??
Why 2 & 7 ?
Thanks! !!

[veraclari]

Hi all, need help as I don’t understand why a method or step is done.

Julian has 5/7 as many marbles as Kenneth. Kenneth has 2/3 as many marbles as Alex. If Alex has 105 more marbles than Kenneth, how mamy more marbles than Julian does Alex Have?

Solution step 1:
5/7 = 10/14 ( convert by multiplying by 2)

2/3 = 14/21 (convert by multiplying by 7)

I know they do the above to find difference in units between Kenneth and Alex. BUT how do we Detemine or Know that must be Multiplied by X 2 & X 7??
Why 2 & 7 ?
Thanks! !!

[andyle.024255sg]

veraclari:

Hi all, need help as I don't understand why a method or step is done.

Julian has 5/7 as many marbles as Kenneth. Kenneth has 2/3 as many marbles as Alex. If Alex has 105 more marbles than Kenneth, how mamy more marbles than Julian does Alex Have?

Solution step 1:
5/7 = 10/14 ( convert by multiplying by 2)

2/3 = 14/21 (convert by multiplying by 7)

I know they do the above to find difference in units between Kenneth and Alex. BUT how do we Detemine or Know that must be Multiplied by X 2 & X 7??
Why 2 & 7 ?
Thanks! !!

For this specific qn, you may not need to convert at all.
Kenneth has 2/3 as many marbles as Alex.
Alex has 105 more marbles than Kenneth
-> Can find Alex's and Kenneth's already, right?

Back to your qn, it is because we are trying to match the units Kenneth has.
J:K
5:7

K:A
2:3

Common multiple of 7 and 2 is 14, hence you convert accordingly.
So, at the end we can write

J:K:A
10:14:21

Cheers.

[veraclari]

Thanks a lot andyle.sg!


Silly me... when u put in e format J: K then I got it. THANKS for your help!!!

[carol73]

hi


pls help

There were 1408 chinese and malay story books in a library. When the librarian bought 73 chinese books and 59 malay books, there were as many chinese books as malay books in the library. how many malay books were there at first?

[carol73]

ariel has a rectangle cardboard that measures 19cm by 15cm. she wants to cut out as many rectangular pieces as she can from it. each small rect piece measures 5cm by 3cm. what is the most number of small rect pieces she can get?