Q&A - PSLE Math

[MathIzzzFun]

genevieve08:

Sorry my first answer is wrong.


But Kelly = $2900 and Susan = $1200 is not right either, working backwards:

First scenario Kelly spent $100 per day and left $500

Taking $2900 - $500 = $2400
2400 / 100 = 24 days

Taking scenario 2 for Kelly

2900 - 2300 = 600
600 / 50 = 12 days

Hi

in scenario 1,
Kelly spent $100 per day, Susan spent $50 per day, Kelly had $500 left.

Amount spent by Kelly = $2900 - $ 500 = $ 2400
Number of days for Kelly to spend $ 2400= $ 2400 / $ 100 = 24 days
Amount spent by Susan = 24 days x $ 50 = $ 1200 --> so Susan spent all her money and Kelly still has $500 left.

In scenario 2,
Kelly spent $50 per day and Susan spent $100 per day, Kelly had $ 2300 left.
Amount spent by Kelly = $2900 - $ $ 2300 = $ 600
Number of days for Kelly to spend $ 600 = $ 600/ $ 50 = 12
Amount spent by Kelly = $ 100 x 12 = $ 1200 --> Susan spent all her money and Kelly still have $ 600 left.

cheers.

[MathIzzzFun]

Winx5015:

Hello,


Following are 2 questions on ratio.

(1). The ratio of Gopal's mass to Siew Leng's mass is 6:5. If Gopal loses 4Kg and Siew Leng gains 3Kg, Siew Leng will be 1Kg heavier than Gopal.
(a). Express siew Leng's mass as a fraction of the total mass.
(b). What is Gopal's actual mass?

(2). Seng Chye and Rani have different amounts of money. If Rani gives $24 to Seng Chye, the ratio of the amount of money she has to what Seng Chye has will be 4:9. If Seng Chye gives $21 to Rani, they will have the same amount of money.
(a). How much more money does Seng Chye have than Rani?
(b). How much money does Rani have?


Thanks!

Hi

Q1.
a) 5/(5+6) = 5/11
b)
Gopal's mass --> 6u, Gopal's mass if he loses 4 kg --> 6u -4
Siew Leng's mass --> 5u, Siew Leng's mass if she gains 3 kg --> 5u + 3
5u + 3 = 6u - 4 + 1
1u = 6
Gopal's mass --> 6u = 36 kg

Q2.

If SC gives R $21, they will have same amount of money, so SC has $42 more than R

R's money --> 1 unit
SC --> 1 unit + $ 42

If R gives SC $24,
R's money : SC's money
-> 1 unit - $ 24 : 1 unit + $42 + $ 24
= 4 : 9

1 unit - $ 24 : 1 unit + 66
= 4 : 9

cross-multiply or equalize:

9 units - $ 216 = 4 units + $264
5 units = $ 480
1 unit = $ 96

SC's money --> 1 unit + $ 42 = $ 138
Rani's money --> 1 unit = $ 96

cheers.

[Winx5015]

Hi MathIzzzFun,


Thanks for solving my questions.

Regards

[anneshirleygilbert]

Can somebody please help with this question?


Four files cost as much as 3 storybooks. Five files cost $7.50 more than 2 storybooks. Mary spent $30 on an equal number of files and storybooks. How many files did she buy?

We tried to find cost of 1 book and cost of 1 file, and got terribly muddled. There must be an easier way. Can somebody help?

[MathIzzzFun]

anneshirleygilbert:

Can somebody please help with this question?


Four files cost as much as 3 storybooks. Five files cost $7.50 more than 2 storybooks. Mary spent $30 on an equal number of files and storybooks. How many files did she buy?

We tried to find cost of 1 book and cost of 1 file, and got terribly muddled. There must be an easier way. Can somebody help?

Hi

1 file --> 3 units
1 story book --> 4 units
1 file + 1 story book --> 7 units

5 files --> 15 units
2 storybooks --> 8 units
7 units = $ 7.50

So, 1 file + 1 story book = $ 7.50
$ 30 / $ 7.50 = 4

Mary bought 4 files and 4 story books

cheers.

[anneshirleygilbert]

Thanks a bunch, MathIzzzFun. You do make it seem so simple.

[MathIzzzFun]

anneshirleygilbert:

Thanks a bunch, MathIzzzFun. You do make it seem so simple.

u r welcome

cheers.

[2DMommy]

Please help me with these questions :


1) In March,the total savings of Andy, Henry, Roy and Zack was $2498. In April, the savings of the four boys became equal after Andy’s savings decreased by $65. Henry’s savings doubled and Roy’s savings increased by
$129. Zack’s savings remained the same. What was Roy’s savings in March ?

2)75% of the children in the stadium were girls. After 52 girls and 4 boys left, the remaining children formed groups of 8. In each group, there were 3 boys. How many children were there in the stadium at first ?

3)A flask is 1/3 filled with chocolate powder. A teapot twice as large as the flask, is 1/4 filled with chocolate powder. Then the flask and the teapot are each filled with water completely and all the contents are mixed together into a chocolate drink. What fraction of the chocolate drink is the chocolate powder?

Thank you.

[tianzhu]

2DMommy:

2)75% of the children in the stadium were girls. After 52 girls and 4 boys left, the remaining children formed groups of 8. In each group, there were 3 boys. How many children were there in the stadium at first ?

Hi

You may use \"Units and Parts\"

At first
Boys: Girls ------- 1u:3u

Change
Boys: Girls ------- -4:-52

In the end
Boys: Girls ------- 3p:5p

Equalise the parts.

(1u - 4) ----- 3p
(x5)
5u - 20 ------ 15p

(3u - 52) ----- 5p
(x3)
9u - 156 ------15p

5u - 20 ----- 9u - 156
4u ----- 136
1u ------ 34

Number of children in the stadium at first ------ 4*34 ------ 136

Best wishes

[tianzhu]

2DMommy:

3)A flask is 1/3 filled with chocolate powder. A teapot twice as large as the flask, is 1/4 filled with chocolate powder. Then the flask and the teapot are each filled with water completely and all the contents are mixed together into a chocolate drink. What fraction of the chocolate drink is the chocolate powder?

Hi

To avoid working with decimals, use 12 units (3 and 4)

Flask(chocolate) ------- 2 units (1/3 of 6 units)
Teapot(chocolate) ------- 3 units (1/4 of 12 units)

Chocolate powder ------ 5 units

Total volume ------- 6+12 ------ 18 units

Fraction of drink which is chocolate --------- 5/18

Best wishes