Q&A - P5 Math

[MathIzzzFun]

redruby:

300 local and 500 foreign stamps are kept in album A. 500 local and 201 foreign stamps are kept in album B. Some stamps are transferred from album B to album A. After the transfer, the number of local stamps is the same as the number of foreign stamps in album A and the number of local stamps is 4 times the number of foreign stamps in album B.

a) Find the number of foreign stamps transferred from album B to album A?
b) Find the total number of stamps transferred from album B to album A?

.. similar question discussedat :
http://www.kiasuparents.com/kiasu/forum/viewtopic.php?f=69&t=280&start=8670


Total, local stamps --> 300 (Album A)+ 500 (Album B)= 800
Total, foreign stamps --> 500 (Album A) + 201 (Album B) = 701
Total, local + foreign stamps --> 1501

after transfer:
Total, local stamps --> 1/2 Album A + 4/5 Album B = 800
Total, foreign stamps --> 1/2 Album A + 1/5 Album B = 701
So, 3/5 Album B --> 800-701 = 99
Album B --> 99/3 x 5 = 165
Album A --> 1501 - 165 = 1336

a) number of foreign stamps transferred from Album B to Album A
--> 201 - 1/5 x 165 = 168

b) Total number of stamps transferred from Album B to Album A
--> 500 + 201 - 165 = 536

cheers.

[MathIzzzFun]

Breadandmuffins:

Mdm goh had 50 pcs of dollar notes. Sme were $2 notes and the rest were $5 notes. The total value of the $2 notes was $40lessthan that of the $5 notes. How may $ 2 notes did Mdm Goh have?


Ans
Assume all $5 notes:
50x $5=$250
$250-$40=$210
$5+$2=$7
$210/7=30 no of $2 notes

There are 30 $2 notes.


I do not understand the last 2 steps. Can someone helpme on that?


Thank u.

suppose we have 2 x $5 and 2 x $2 (difference in value = $6), and we replace the 1x $2 with 1 x$5 (still keeping the total number of notes to 4),
you see that the difference in value = $ 13 --> increase of $7, because
-- when 1 x $5 is added --> value of $5 increased by $5
-- 1 x $2 removed --> value of $2 reduced by $2
so the net effect is the difference increased by $7 .... this is the same if we were to replace 1 x $5 with $2 the difference will reduced by $7

(*pictorial explanation of a similar question at http://tinyurl.com/mathizzzfun-assumption)

In solution provided, it is assumed that all are $5, so the difference in value = $ 5 x 50 - $0 (since no $2 notes) = $250
The actual difference in value is $ 40
So, we need to reduce the difference by $ 250 - $40 = $210, by replacing the $5 with $2.

since replacing 1 x$5 with 1 x$2 will reduce the difference by $7

The number of $2 notes --> $210/$7 = 30

cheers.

[redruby]

MathIzzzFun:

redruby:

300 local and 500 foreign stamps are kept in album A. 500 local and 201 foreign stamps are kept in album B. Some stamps are transferred from album B to album A. After the transfer, the number of local stamps is the same as the number of foreign stamps in album A and the number of local stamps is 4 times the number of foreign stamps in album B.

a) Find the number of foreign stamps transferred from album B to album A?
b) Find the total number of stamps transferred from album B to album A?

.. similar question discussedat :
http://www.kiasuparents.com/kiasu/forum/viewtopic.php?f=69&t=280&start=8670


Total, local stamps --> 300 (Album A)+ 500 (Album B)= 800
Total, foreign stamps --> 500 (Album A) + 201 (Album B) = 701
Total, local + foreign stamps --> 1501

after transfer:
Total, local stamps --> 1/2 Album A + 4/5 Album B = 800
Total, foreign stamps --> 1/2 Album A + 1/5 Album B = 701
So, 3/5 Album B --> 800-701 = 99
Album B --> 99/3 x 5 = 165
Album A --> 1501 - 165 = 1336

a) number of foreign stamps transferred from Album B to Album A
--> 201 - 1/5 x 165 = 168

b) Total number of stamps transferred from Album B to Album A
--> 500 + 201 - 165 = 536

cheers.

Thanks.

[redruby]

Marcus had some marbles. He kept 3/10 of them and gave the rest to his new buddies. Sebastian and Derrick. In the end, Marcus had 298 fewer marbles than Sebastian but 122 more marbles than Derrick. How many marbles did Marcus have at first?

:?

[2632parent]

Can anyone help me in this question?

1) Seven years ago, Mdm Aminah was 5 times as old as her son. Their total age now is 62. What is Mdm Aminah present age? :?


:thankyou: :udawoman:

[jieheng]

2632parent:

Can anyone help me in this question?

1) Seven years ago, Mdm Aminah was 5 times as old as her son. Their total age now is 62. What is Mdm Aminah present age? :?


:

Seven years ago ,

their total age = 62 - 2*7 = 48

Mdm Aminah 5u
Her son 1u

5u + 1u -> 48
6u -> 48
1u -> 8

Mdm Aminah's present age is 5u + 7 = 5*8 + 7 = 47

[redruby]

quekcc:

redruby:

Marcus had some marbles. He kept 3/10 of them and gave the rest to his new buddies. Sebastian and Derrick. In the end, Marcus had 298 fewer marbles than Sebastian but 122 more marbles than Derrick. How many marbles did Marcus have at first?

:?

Assuming at first, Marcus had 10 units

Then, Marcus kept 3 units, and the rest were given to Sebastian and Derrick.

Sebastian had 3 units + 298, and Derrick had 3 units - 122

So total is 6 units + 298 - 122 = 6 units + 176

Since that is enough to 7 units, 1 unit will be 176 marbles.

So at first, Marcus had 1760 marbles.

Thanks.

[chloecube]

Jamesbond:

Pl help me solve (b) & (c).

Hi

The answers are

(b) 45 , follow this pattern (n+1)(n+2)/2

(c) pattern 13 , follow this (n+1)(n+1)

n ----- pattern number

Best wishes[/quote]

Still my ds is not able to follow up...can u pl explain tianzhu....[/quote]
Hi

For (b), take the pattern number, in this case 9

Sorry, the sequence is n*(n+1)/2

(9)*(9+1)/2 ------- 9*10/2 --- 90/2 ------ 45

For total, the sequence is ( n+1)*(n+1)

196 ------ 14*14

Hence pattern number is 13.

I am going out. Please let me know if you need more information.I'll do it later

Best wishes[/quote]

sorry, i have been thinking abt this sum the whole afternoon but cant seem to figure out

is this a standard formula for solving such question?
eg n=n(n-1)+1
n(n+1)/2 (seen another similar question with such formula)
Pattern 1 - 1
Pattern 2 - 3
Pattern 3 - 6
Pattern 4 - 10
what is Pattern 9?
answer is 45 by using this formula n(n+1)/2
so when do i use n(n+1)/2 and when do i use n=n(n-1)+1
i am confused here :faint:

[kiasuMay11]

MathIzzzFun:

kiasuMay11:

Ann made some cupcakes. If she pack them into boxes of 9 cupcakes each, she would have 3 cupcakes left. If she packed them into boxes of 7 cupcakes each, she would be short of 4 cupcakes for the last box. If she made less than 100 cupcakes, how many cupcakes were there?


Pls help.

If she packed them into boxes of 7 cupcakes each, she would be short of 4 cupcakes for the last box --> 3 cupcakes in the last box ie 3 left.

So, in both cases, there were 3 cupcakes left.
suppose we remove the 3 cupcakes, then the remaining number of cupcakes can be packed into boxes of 7 or boxes of 9 exactly.

Lowest common multiple of 7 & 9 --> 63
the total number of cupcakes = 63 + 3 (add the 3 cupcakes that were removed) = 66

cheers.

Tq, it looks so easy after u have explain.

[Oracle]

Here’s another question I need help:


Gerry had a total of 30 pens and pencils at first. He then decided to exchange all his pens for pencils. If he exchanged every pen for 2 pencils, he would have 48 pencils. How many pens and pencils did he have at first?

Thank you very much.