Q&A - PSLE Math

[tianzhu]

jewelbox:

1. Class A and Class B have the same number of pupils. The ratio of the number of boys in Class A to the number of boys in Class B is 3:2. The ratio of the number of girls in Class A to the number of girls in Class B is 3:5. Find the ratio of the number of boys in Class A to the number of girls in Class B. Ans: 6:5

Hi

In this question, a student needs to see that the ratios representing the boys and girls are of different measures and kinds. One needs to differentiate the ratios showing boys and girls.

Let’s have units for boys and parts for girls.MD would come in handy for this question. Due to time constraints, I am not drawing it, but shall give you some pointers.

Boys ----- A : B ------ 3u : 2u
Girls ----- A : B ------ 3p : 5p

Class A and Class B have the same number of pupils.

3u + 3p ----- 2u + 5p
Hence, 1u ----- 2p

Boys ----- A : B ------ 6p : 4p
Girls ----- A : B ------ 3p : 5p

The ratio of the number of boys in Class A to the number of girls in Class B ----- 6:5

Best wishes

[tianzhu]

jewelbox:

2.I have some red and blue ribbons in a bottle. if I add in 20 red ribbons, 60% of my ribbons are blue. If i add in another 60 blue ribbons, 75% of my ribbons are blue. How many ribbons have I in the bottle. Ans: 180 ribbons

Hi

This question was discussed in our earlier posts. Depending on one’s interpretation of the word another in the second condition, one may end up with 180 or 80.

Please confirm with your teacher.

Condition1
Red : Blue -------- change add 20 red ribbons
2u:3u

Condition 2
Red : Blue -------- change add 60 blue ribbons
1p:3p

2u – 20 ------ 1p
3u+60 -------3p

Equalising the parts

6u – 60 -------3p

3u+60 ------- 6u-60
3u ------ 120
1u ------ 40

Number of ribbons at first ------ (5*40)-20 ------180

Please refer to an example for a similar question.

Best wishes

http://farm8.staticflickr.com/7146/6728816353_e2a7aca824_z.jpg\">

[Winx5015]

Hi,


Got problem with the following question. Pse help.

A coin box contained some 10-cent coins and 50-cent coins in the ratio of 7:2. Peter took out eight 10-cent coins and put in another twenty 50-cent coins into the box. There are now half as many 10-cent coins as 50-cent coins.
(a) How many 10-cent coins were in the box at first?
(b) What is the total value of all the coins in the box now?

Thanks!

[tianzhu]

Winx5015:

Hi,


Got problem with the following question. Pse help.

A coin box contained some 10-cent coins and 50-cent coins in the ratio of 7:2. Peter took out eight 10-cent coins and put in another twenty 50-cent coins into the box. There are now half as many 10-cent coins as 50-cent coins.
(a) How many 10-cent coins were in the box at first?
(b) What is the total value of all the coins in the box now?

Thanks!

Hi

You may use \"Units and Parts\"

At first
10-cent coins: 50-cent coins ------- 7u:2u

Change
10-cent coins: 50-cent coins ------- -8 :+20

In the end
10-cent coins: 50-cent coins ------- 1p:2p


Equalise the parts.

(7u - ----- 1p
(x2)
14u - 16 ------ 2p

(2u + 20) ----- 2p

14u - 16 ----- 2u + 20
12u ----- 36
1u ------ 3

Number of 10-cent coins were in the box at first ------ 3*7 ------ 21

Now
Number of 10-cent coins ------ 13
Number of 50-cent coins ------- 26

Total value ------- $14.30

Best wishes

[2DMommy]

Please help me with these questions :


1) Benita and Mildred shared a box of laminating sheets. If Benita were to give 25% of her share to Mildred, Benita would have half of Mildred's final share. If Benita were to give 16 laminating sheets to Mildred, Benita would have 54 fewer laminating sheets than Mildred. If they were to pack all their laminating sheets into boxes of 25 each, what is the least number of boxes required to pack all of them ?

2)Jan and Kay had equal number of sweets and equal number of chocolates. Jan ate 12 sweets and Kay ate 18 chocolates and then the ratio of Jan's sweets to chocolates became 1 : 7 and the ratio of Kay's sweets to chocolates became 1 : 4. How many sweets did Jan have at first?

3)The tickets for a show are priced at $10 and $5. The number of ten-dollar tickets available is 1 half times the number of five-dollar tickets. 5 out of 6 ten-dollar tickets and all the five-dollar tickets were sold. The amount of money collected from the sale of the tickets were $5600. How much more would have been collected if all the tickets were sold ?

:thankyou:

[Bunny27]

I’m not sure about tis question…

Colin and Karin save $2378.1/6 of Colin’s savings is $41 more than 1/7 of Karin’s savings. Find the ratio of Colins savings to Karin’s savings. Express your answer in the simplest form.

TIA

[Winx5015]

Hi tianzhu,


Thanks for your solution.

Have a nice weekends

[jewelbox]

Hi tianzhu

Thank you so much for the solutions and teaching how to use units and parts.:)

[tianzhu]

Winx5015:

Hi tianzhu,


Thanks for your solution.

Have a nice weekends

Hi

You're welcome.

Have a good weekend too.

Best wishes

[tianzhu]

jewelbox:

Hi tianzhu

Thank you so much for the solutions and teaching how to use units and parts.:)

Hi

You're welcome.

Your username reminds me that my jewelbox is very empty, so sad.

While MD may be used to solve your question, I think UP is more efficient.

Have a good weekend.

Best wishes