Q&A - PSLE Math

[Sarah]

thanks Chief for the working.


Need help for the following $ questions.

Question 1
the ration of $2 notes to 50-cent coins in Mabel’s piggy bank was 13:8. She exchanged 24 pieces of $2 notes for some 50-cent coins, after which, the ratio of $2 notes to 50-cent coins became 1:8. What was the total value of $2 notes and 50-cent coins in the piggy bank at first?

Question 2
the ration of $5 notes to 20-cent coins in Mr Tan/ counter was 19:5. Mr Tan exchanged 15 of his $5 notes for some 20-cent coins. The ratio of the $5 notes to 20-cent coins then became 1:5. What was the total value of $5 notes and 20-cent coins at first?

Question 3
a box contained 50-cent coins and 20-cent coins in the ratio of 2:3. Peter took out four 50-cent coins, exchanged them for 20-cents and put the money back into the box. The ratio then became 2:7. Find the sum of money in the box at first.

thanks for helping, exam is coming, u know.

[Priskhipo]

HI Sarah,


The 3 questions share similar strategy.

http://www.postimage.org/image.php?v=gx1Rl8GA

http://www.postimage.org/image.php?v=Pq25SceS

http://www.postimage.org/image.php?v=Pq25SrcJ

[youngmum]

For the above question 1 - for step 1 why 12 + 24? I don't understand the first step, the rest ok. Pls explain to me. Thanks.


i solved it the ratio way though.

13: 8 = 39 : 24
1:8 = 15:120

So, 39 x 2 = 78
24/2 = 12

total = 78 + 12 = 90

[ChiefKiasu]

Priskhipo:

HI Sarah,


The 3 questions share similar strategy.
...

Priskhipo, thanks for the detailed \"workout\"!

[heutistmeintag]

Priskhipo, may I know if you are a teacher or tuition teacher? Your answers are so professional. Do you take students?

[lantian]

http://farm4.static.flickr.com/3252/2887152891_1a46c5c3de_o.jpg\">

[Priskhipo]

heutistmeintag:

Priskhipo, may I know if you are a teacher or tuition teacher? Your answers are so professional. Do you take students?

Hi heutistmeintag,

Thanks you. I'm a teacher but not in the mainstream kind.
Sorry, I'm not taking in any students for tuition.
I'm glad to be able to help out in this website and continue to do so if time permit.

[Priskhipo]

youngmum:

For the above question 1 - for step 1 why 12 + 24? I don't understand the first step, the rest ok. Pls explain to me. Thanks.


i solved it the ratio way though.

13: 8 = 39 : 24
1:8 = 15:120

So, 39 x 2 = 78
24/2 = 12

total = 78 + 12 = 90

Compare the orange bar (13 small units) to the bar consists of blue rectange (1 small unit) with green and white dotted-line rectangles.

The difference is indicated by the arrow (12 units).
The green rectangle represents 12 number and the white dotted-line rectangle represents 24 number.

Therefore 12 units represent 12 + 24 = 36

[lantian]

Sarah:

Q2. A, B and C are three numbers. The average a, B and C is 5 greater tha the averaga of A and b. If C is 38, find the total of A, B and C.

http://farm4.static.flickr.com/3010/2898264072_99252aab49_o.jpg\">

[ChiefKiasu]

lantian:

http://farm4.static.flickr.com/3010/2898264072_99252aab49_o.jpg\">

Sigh... I'm still trying to learn to think like you