Maths Problem (Percentage)

[Symantec9]

Hi 2 every1...gota maths problem n need all shifu here 4 help...

 

Q: Siti had some red n blue pens. 80% of d pens were red. After she bought another 63 red pens n 46 blue pens, 75% of d pens were red. Find d total nbr of pens she had @ 1st.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Kam siah...

 

 

 

 

 

 

 

 

 

 

 

Answer is 375pens, but dun noe how 2 get dat nbr...

Edited June 10, 2008 by Symantec9

[Tploh]

Let R = number of initial Red pens. B = number of initial Blue pens.

 

So, statement (1) :

R

----- = 80%

(R+B)

 

thus,

R = 0.8R + 0.8B

0.2R = 0.8B

R = 4B

 

Statement (2) :

 

R + 63

------------------- = 75%

( R + 63 + B + 46 )

 

and replace R with 4B in statement (2) and become

 

4B + 63

-------------------- = 75%

( 4B + 63 + B + 46 )

 

 

4B + 63 = 0.75 ( 5B + 109 )

4B + 63 = 3.75B + 81.75

0.25B = 18.75

B = 75

 

Then solve for R,

R = 4B = 300

 

So, R + B = 375.

[Mivec9]

Given:

Blue = 20/100 = 1/5

Red = 80/100 = 4/5

 

Hence, Blue = 1U (unit)

Red = 4U (unit)

--------------------------------------

 

After adding new pens, we have:

 

Blue = 1U + 46 = 1 Unit

Red = 4U + 63 = 3 Unit

 

Therefore, 3(1U + 46) = 4U + 63

3U + 138 = 4U + 63

4U - 3U = 138 - 63

1U = 75

5U = 75 X 5 = 375 (ans)

Edited June 10, 2008 by Xtraun

[Albeniz]

I used the same approach and arrived at the same conclusion.

 

Agrees well.

[Symantec9]

TQ bro Tploh, greatly appreciated yr help n explanation

[Symantec9]

Thanks, bro Xtraun, great explanation, really appreciated, cheers.

[Symantec9]

Hi bro Albeniz, thank u 4 d seconded, hv a great day.

[Tomcat]

the 2 questions you posted...which level huh? think you have to translate the answers to 'modeling' methods for primary school...heeeheee...

[Mivec9]

P6...his kid preparing for psle, i guess. if not, he is a super duper tutor

[Tomcat]

maybe should have a sub section to lite & ez...maths problems for primary 6...for people like me and him to post... ...btw, i am not a tutor

[Friendstar]

i can only use algebra to solve....

[Scenic98]

Given:

Blue = 20/100 = 1/5

Red = 80/100 = 4/5

 

Hence, Blue = 1U (unit)

Red = 4U (unit)

--------------------------------------

 

After adding new pens, we have:

 

Blue = 1U + 46 = 1 Unit

Red = 4U + 63 = 3 Unit

 

Therefore, 3(1U + 46) = 4U + 63

3U + 138 = 4U + 63

4U - 3U = 138 - 63

 

tks for the enlightenment. i think your method is the one that's being taught to the kids these days. back then, we were all taught using the other method mentioned earlier.

 

 

1U = 75

5U = 75 X 5 = 375 (ans)

[Mivec9]

I know, u told me before. Anyway...these are typical questions that u need make sure your kid can answer. For TS other question...it is similar to this Qn. Apparently, it seems he has not grasp the essence yet

[Mivec9]

yes u r rite.

 

Back our days, we were struggling with purely boxes stuff and strictly no algebra...it was a miracle i made it then!

[Scenic98]

but i can't recall me doing such questions when i was at P6 27 years ago. some more i got A*

[Tomcat]

cos now they looking for superstar mah...like media corp...

[Kopi_peng]

Given:

Blue = 20/100 = 1/5

Red = 80/100 = 4/5

 

Hence, Blue = 1U (unit)

Red = 4U (unit)

--------------------------------------

 

After adding new pens, we have:

 

Blue = 1U + 46 = 1 Unit

Red = 4U + 63 = 3 Unit

 

Therefore, 3(1U + 46) = 4U + 63

3U + 138 = 4U + 63

4U - 3U = 138 - 63

1U = 75

5U = 75 X 5 = 375 (ans)

 

these days, when given such question, one has to start drawing bars and observe the 'relationship', ie, in this case, 4/5 plus 1/5 and 3/4 plus 1/4. from there, they solve the problem with only 1 unknown.

[Thug]

If u experiencing some difficulties in teaching someone mathematic in pri level...check out this site.

http://www.pennsford.com/

My gf went as she is a full time private tutor...not bad though...