Q&A - PSLE Math

[tianzhu]

Spongy:

Hi I have 2 questions to ask, thanks in advance.


1.Aunt May baked some square, round and oval cookies. For every 3 square cookies that were baked, 2 round cookies were baked. For every 4 square cookies that were baked, 3 oval cookes were baked.
(a) Find the ratio of the number of square cookies to round cookies to oval cookies baked.
(b) After Aunt May baked another 120 round cookies, 30% of the cookies now were round cookies. How many square cookies did Aunt May Bake?

Hi

Square:Round ------ 3:2 -------- 12:8

Square:Oval ------- 4:3 ------- 12:9

The units for “Square cookies” are repeated in both set of ratios, so make them the same.

Ratio of the number of square cookies to round cookies to oval cookies baked ------- 12:8:9

Squre cookies ------- 12 units
Round cookies ------- 8 units + 120
Oval cookies ------- 9 units

8 units + 120 ------- 30%

21 units ------- 70%

3 units ------- 10%

Hence, 8 units + 120 ------- 9 units

This gives 1 unit ------- 120

Number of square cookies --------12*120 ------1440

Best wishes

[tianzhu]

Spongy:

2.Mr Lim earned $3000 monthly,which was 20% more than the monthly salary of Mr Tan
(a) What was Mr Tan's monthly salary?
(b) When both Mr Lim's and Mr Tan's monthly salaries were increased by the same percentage, Mr Lim earned $590 more than Mr Tan. What was the percentage increase in their salaries?

Hi

120% -------3000

10% ------- 250

100% ------ 2500 (Mr Tan’s salary)

Difference in salary ------ 3000 – 2500 ------ 500

10% of 3000 ------- 300
10% of 2500 ------ 250

Every increase of 10% in salary, the difference is $50

10% ------- $50
2 % ------- $10
18% ------ $90 (590-500)

% increase in salary ------- 18%

Check
118% of 3000 ------- 3540
118% of 2500 ------ 2950
3540 – 2950 ------ 590

Best wishes

[MathIzzzFun]

Spongy:

Hi I have 2 questions to ask, thanks in advance.



2.Mr Lim earned $3000 monthly,which was 20% more than the monthly salary of Mr Tan
(a) What was Mr Tan's monthly salary?
(b) When both Mr Lim's and Mr Tan's monthly salaries were increased by the same percentage, Mr Lim earned $590 more than Mr Tan. What was the percentage increase in their salaries?

Hi

Another approach for (b)

When the salaries are increased by the same percentage, the difference in salaries will also increase by the same percentage.
eg. 15% increase in the both salaries
new salary of Mr Tan --> 115% Tan
new salary of Mr Lim --> 115% Lim
difference --> 115% (Lim - Tan) ie the difference in salaries also increase by 15%.

original difference --> $3000 - $2500 = $500
New difference --> $ 590
so, % increase in salary --> $90/$500 x 100% = 18%

cheers.

[isetan]

tianzhu:

Hi


Here’s another way to look at the candle question.

Life is just like a candle in the wind.

As I get older, I start to appreciate more the fragility and uncertainty in life.

We are just a flame atop a candle.

A draft from an unseen corner may put an end to it.

Best wishes

[img]http://farm9.staticflickr.com/8151/7158587127_c44efa4cf1_z.jpg[/
]

Thanks Tianzhu!

[SAHM88]

1. A car left Town X for Town Y at the same time when a motorcycle left Town Y for Town X. The average speed for the car is 88km/h while the average speed of the motorcycle was 64km/h. The two vehicles passed each other at a point 33km from the midpoint between Town X and Town Y.

What was the distance between Town X and Town Y?


2. There were 225 apples and 253 oranges in Box A.
There were 260 apples and 212 oranges in Box B.
Mr Chia moved some apples and oranges from Box B to Box A.
In the end, 40% of the fruits in Box A and 70% of the fruits in Box B were apples. How many fruits did Mr Chia move from Box B to Box A?

[Chan09]

Need help

S works together with A and take 10 days to produce an art piece. If the 2 girls first work together for 4 days, followed by S working alone for 10 days, A will take another 5 days to complete the remaining work. How long will each girl take to produce the art piece without the involvement of the other party?

I understand the first part as that fraction when both girls work together for 4 days followed by S working alone for 10 days and A working alone for 5 days = fraction when both girls work together for 9 days followed by S working alone for 5 days (but not S working for 5 days??)

Ans: S takes 50 days and A takes 12.5 days.

[2cor41618]

Chan09:

Need help

S works together with A and take 10 days to produce an art piece. If the 2 girls first work together for 4 days, followed by S working alone for 10 days, A will take another 5 days to complete the remaining work. How long will each girl take to produce the art piece without the involvement of the other party?

I understand the first part as that fraction when both girls work together for 4 days followed by S working alone for 10 days and A working alone for 5 days = fraction when both girls work together for 9 days followed by S working alone for 5 days (but not S working for 5 days??)

Ans: S takes 50 days and A takes 12.5 days.

Both (A+S)-->10 days---1 art piece
Both (4 days) + S(10 days) + A (5 days)--> 1 art piece
The highlighted above is the same as:
Both (9 days) + S (5 days)--> 1 art piece

Both (9 days)--> 9/10 of art piece, thus
S (5 days) --> 1/10 of art piece, so
S will take 5 x 10 = 50 days to complete 1 art piece.

Looking at the highlighted equation, if we substitute S (10days) as 2/10 of a art piece and both (4days) as 4/10 of a art piece, then,

A (5 days)--> 4/10 of a art piece, so
A will take 5 x 10/4 = 12.5 days to complete 1 art piece.

Hope this helps

[MathIzzzFun]

SAHM88:

1. A car left Town X for Town Y at the same time when a motorcycle left Town Y for Town X. The average speed for the car is 88km/h while the average speed of the motorcycle was 64km/h. The two vehicles passed each other at a point 33km from the midpoint between Town X and Town Y.

What was the distance between Town X and Town Y?


2. There were 225 apples and 253 oranges in Box A.
There were 260 apples and 212 oranges in Box B.
Mr Chia moved some apples and oranges from Box B to Box A.
In the end, 40% of the fruits in Box A and 70% of the fruits in Box B were apples. How many fruits did Mr Chia move from Box B to Box A?

Hi

Q1.
Speed ratio of the car and motorcycle --> 88 : 64 = 11 : 8
Total distance --> 19 units
Difference in distance travelled --> 3 units

When both vehicles meet, the car has travelled 33 km x 2 = 66 km more than the motorcycle.

So, 3 units --> 66 km, 19 units --> 418 km

Distance between Town X and Town Y = 418 km

Q2.

http://i46.tinypic.com/2h2easg.png\">

cheers.

[AJH]

Hi - I’m not sure how to do this :


Mr Kim bought some chocolates for his grandchildren. If he gave each grandchild 7 chocolates, the last grandchild would only get get 3 chocolates. If he gave each grandchild 5 chocolates, he would have 20 chocolates left. How many grandchildren does Mr Kim have?

Thank you.

[MathIzzzFun]

Chan09:

Need help

S works together with A and take 10 days to produce an art piece. If the 2 girls first work together for 4 days, followed by S working alone for 10 days, A will take another 5 days to complete the remaining work. How long will each girl take to produce the art piece without the involvement of the other party?

I understand the first part as that fraction when both girls work together for 4 days followed by S working alone for 10 days and A working alone for 5 days = fraction when both girls work together for 9 days followed by S working alone for 5 days (but not S working for 5 days??)

Ans: S takes 50 days and A takes 12.5 days.

Hi

using UP (units & parts)

S --> 10u ie 1u/day
A--> 10p ie 1p/day

Total --> 10u + 10p


S&A work 4 days,S works 10 days, A works 5 days
--> 4u+4p+10u+5p = 14u+9p

so, 10u + 10p = 14u + 9p, 1p = 4u

Total
--> 10u + 40u = 50u --- S takes 50 days
--> 10p +10/4p = 12.5p --- A takes 12.5 days

cheers.