Q&A - PSLE Math

[atutor2001]

stary:

Hi all,


Have a question to ask u all...

There were some fruits in a warehouse. 3/7 of them were apples and the rest were oranges. After throwing away 27 apples and 1/4 of the oranges that were rotten, there were 3/5 of the fruits left.
(a) How many fruits were thrown away?
(b) How many apples were there at first?

:?

Using ratio to solve :

Apple : Orange : Total = 3 : 4 : 7 (Before)
Because the fruits left is given as 3/5 of \"Before\", the total of \"before\" must be divisible by 5. So x 5 to the ratio

Apple : Orange : Total = 15U : 20U : 35U (Before)
Apple : Orange : Total = -27 : -5U : (??) (Fruits thrown away)
Apple : Orange : Total = (15U-27) : 15U : 21U (After)

The decrease in the total is 35U - 21U = 14U
The fruits thrown away is 27+5U

Therefore, 14U = 27 + 5U
9U = 27
U = 3

Total fruits thrown away is 14U = 42
Total apples (at first) is 15U = 45

[stary]

atutor2001:

stary:

Hi all,


Have a question to ask u all...

There were some fruits in a warehouse. 3/7 of them were apples and the rest were oranges. After throwing away 27 apples and 1/4 of the oranges that were rotten, there were 3/5 of the fruits left.
(a) How many fruits were thrown away?
(b) How many apples were there at first?

:?

Using ratio to solve :

Apple : Orange : Total = 3 : 4 : 7 (Before)
Because the fruits left is given as 3/5 of \"Before\", the total of \"before\" must be divisible by 5. So x 5 to the ratio

Apple : Orange : Total = 15U : 20U : 35U (Before)
Apple : Orange : Total = -27 : -5U : (??) (Fruits thrown away)
Apple : Orange : Total = (15U-27) : 15U : 21U (After)

The decrease in the total is 35U - 21U = 14U
The fruits thrown away is 27+5U

Therefore, 14U = 27 + 5U
9U = 27
U = 3

Total fruits thrown away is 14U = 42
Total apples (at first) is 15U = 45

Thanks! :thankyou:

[Saralala]

tianzhu:

1) There were some marbles at a shop. The ratio of the number of red marbles to the number of blue marbles was 2:3. When 50 more red marbles and 30 more blue marbles were added, the ratio of the number of red marbles to the number of blue marbles became 5:6. How many marbles were there at first?

Let me try to solve the first question:

Method 1:

If you use algebra, it will be rather fast (trained my son to do so as PSLE still allows):

2x + 50 = (5/6) (3x +30)
x = 50

5 units at the start so 50 x 5 = 250 marbles at first.

-----------------------------------------------------------------
Method 2 (Diagrams):

Draw 2 units for red and 3 units for blue.

For red, draw dotted unit for 50 extra red and a 1 unit size to fill up 5:6 to become 6:6.

For blue, just add 30 extra blue as dotted unit.

Thus, 30 + 1 big unit = 50 + 1 small unit

We can say 1 big unit - 1 small unit = 20.

--- Look at red units now. There are 2 big units and 1 50 dotted unit. So 2 small units + 20 + 20 +50 = 5 small units.

3 small units = 90
1 small unit = 30

2 big unit = 30 x 5 - 50
= 100

5 big units = 100/ 2 * 5
= 250.

Alright, sorry if it sounds very difficult, but I don't think it is if I can draw. Haha. Too lazy to draw. :x

[Hifive]

Hi all,


Need help with this question:

During a basketball match, the teacher promised the team of 8 pupils an equal playing time during the 40 minutes match. Given that only 5 players can play at any one time, what is the average playing time for each pupil?

Thanks in advance.

[MathIzzzFun]

Hifive:

Hi all,


Need help with this question:

During a basketball match, the teacher promised the team of 8 pupils an equal playing time during the 40 minutes match. Given that only 5 players can play at any one time, what is the average playing time for each pupil?

Thanks in advance.

Hi

Divide 40 minutes into 8 x 5 minutes time slots, and for each 5 min slot, there will be 5 playing slots, total 5 x 8 playing slots. So, each will get 5 playing slots ie 5 x 5 = 25 min.

http://i55.tinypic.com/24cd3r4.jpg\">

cheers.

[Hifive]

Hi MathIzzzFun


Thanks for your explanation.

Have a nice day ahead!

[alrama]

Kailing and jim had a total of $63. Kailing gave 0.3 of her share to jim. Jim then gave 1/3 of the total amount of money he had to his brother. In the end, all the three children had the same amount of money. How much money did kailing have at first? ans:36. Can anyone explain?

[MathIzzzFun]

Hifive:

Hi MathIzzzFun


Thanks for your explanation.

Have a nice day ahead!

u r welcome

cheers.

[bobsg01]

Need help to find Angle m


Thanks in advance for your help.

http://i55.tinypic.com/105z3lz.jpg\">

[atutor2001]

bobsg01:

Need help to find Angle m


Thanks in advance for your help.

http://i55.tinypic.com/105z3lz.jpg\">

I think the easiest way to solve is using \"rotation'.

Imagine that square SWXY and STUV are actually the same square.

Square STUV is the new position of SWXY when it is rotated 35 degree anti-clockwise.

Note :
line SY corresponds to line SV. After SY has rotated 35 degree anti-clockwise, it becomes SV
line SW corresponds to line ST. After SW has rotated 35 degree anti-clockwise, it becomes ST.

Therefore, angle WST = 35 degree


Then focus on square SPQR.

angle PST + angle WST + angle WSR = 90
30 + 35 + m = 90
m = 25