Q&A - PSLE Math

[jieheng]

iamproudparents:

2)The ratio of the number of marbles John had to the number of marbles Benny had at first was 2:3. After John gave 18 of his marbles to Benny, John had 3/5 the number of marbles Benny had. How many more marbles did Benny have than John at first?

2)

At first...............After John gave 18 of his marbles to Benny
John 2u ....................John 3u
Benny 3u ...................Benny 5u
Total 5u ....................Total 8u

As total no of marbles (before and after John gave 18 of his marbles to Benny) remains the same , change the total no to the common multiple , 40u .

At first...............After John gave 18 of his marbles to Benny
John 2u*8 = 16u ....................John 3u*5 = 15u
Benny 3u*8 = 24u ...................Benny 5u*5 = 25u
Total 5u*8 = 40u ....................Total 8u*5 = 40u

16u - 15u --> 18
1u --> 18

24u - 16u = 8u = 8*18 = 144

Benny had 144 more marbles than John at first

[jieheng]

iamproudparents:

3)Helen had 30 marbles fewer than Sam. After Sam gave Helen 100 marbles , Helen had twice as many marbles as Sam. How many marbles did Sam have at first?

S [---------1u------------][30]
H [---------1u------------]

S [-----1p--------][--70--][30]
H [-----1p--------][--70--]

After Sam gave Helen 100 marbles

S [-----1p--------]
H [-----1p--------][--70--][---100---]

Helen had twice as many marbles as Sam

1p --> 70 + 100 = 170

1p +70 + 30 --> 170 + 70 + 30 = 270

No of marbles that Sam had at first = 270

[jieheng]

iamproudparents:

4)Sally's monthly salary is $500 more than Betty but their monthly expenditure are the same. Over a period of time, Sally has saved $2700 but Betty has only saved $200. If each of them spends $740 a month. What is Sally's monthly salary?

Over a period of time ,

the difference in savings = 2700 - 200 = 2500

No of months for Sally to save $2700 = 2500/500 = 5

Amount of momey that Sally saved per month = 2700/5 = 540

540 + 740 = 1280

Sally's monthly salary = $1280

[jieheng]

iamproudparents:

5)Kenny and Joo Seng are selling durians at a fruit stall. If Kenny sells 60 durians per day and Joo Seng sells 15 durians per day, Kenny will have 24 durians left when Joo Seng has sold all his durians.

if Joo Seng sells 60 durians per day and Kenny sells 15 durians per day, Kenny will have 204 durians left when Joo Seng has sold all his durians.

a)How many durians does Kenny have?

b)If the durians are sold at 4 for $10, how much money will they earn after selling all their durians?

If Kenny sells 60 durians per day and Joo Seng sells 15 durians per day, Kenny will have 24 durians left when Joo Seng has sold all his durians.

K [------][------][------][------][24]
J [------]

if Joo Seng sells 60 durians per day and Kenny sells 15 durians per day, Kenny will have 204 durians left when Joo Seng has sold all his durians.

K [][][][][][][][][][][][][][][][][24] (16u + 24)
J [][][][] (4u)

16u + 24 - 1u --> 204
1u --> 12

a) no of durians that Kenny has = 16u + 24 = 16*12 + 24 = 216


b) total no of durians = 16u + 24 + 4u = 20u + 24 = 20*12 + 24 = 264


the amount of money that they will earn after selling all their durians
=264/4 * $10
=$660

[ozora]

Need help: father ->when I was your age you were 3 years old.

Son-> when I become your age you will be 63 years old. How old is the father And son respectiveLy now?

[MathIzzzFun]

ozora:

Need help: father ->when I was your age you were 3 years old.

Son-> when I become your age you will be 63 years old. How old is the father And son respectiveLy now?

http://i46.tinypic.com/1ekkmw.png\">


cheers

[ozora]

MathIzzzFun:

ozora:

Need help: father ->when I was your age you were 3 years old.

Son-> when I become your age you will be 63 years old. How old is the father And son respectiveLy now?

http://i46.tinypic.com/1ekkmw.png\">


cheers

Thanks maths

[mama_10]

Hi,


Need help in this question.
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 girks in Class B is 3:5. Find the ratio of the number of boys to the number of girls in Class A.

Thank you!

[MathIzzzFun]

mama_10:

Hi,


Need help in this question.
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 girks in Class B is 3:5. Find the ratio of the number of boys to the number of girls in Class A.

Thank you!

Since the Class A and Class B have same number of pupils, the difference between number of boys in A and B, and the difference between the number of girls in A and B, must be the same.

Boys --> Class A : Class B = 3 : 2 = 6 : 4
Girls --> Class A : Class B = 3 : 5
ratio of number of boys to number of girls in A = 6 : 3 = 2 : 1


http://i45.tinypic.com/15gc6qs.png\">

cheers.

[mama_10]

MathIzzzFun:

mama_10:

Hi,


Need help in this question.
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 girks in Class B is 3:5. Find the ratio of the number of boys to the number of girls in Class A.

Thank you!

Since the Class A and Class B have same number of pupils, the difference between number of boys in A and B, and the difference between the number of girls in A and B, must be the same.

Boys --> Class A : Class B = 3 : 2 = 6 : 4
Girls --> Class A : Class B = 3 : 5
ratio of number of boys to number of girls in A = 6 : 3 = 2 : 1


http://i45.tinypic.com/15gc6qs.png\">

cheers.

Sorry, I dont understand why change the Boys ratio from 3:2 to 6:4?
thank you