Q&A - PSLE Math

[MathIzzzFun]

kwcllf:

Hi, please help.


2 buses, A and B, travel from the same end of the road at the same time in the same direction. After travelling 6 minutes, Bus A overtakes a cyclist. 2 minutes later, Bus B overtakes the same cyclist. If A and B travel at an average speed of 1000m/min and 800m/min respectively, what is the average speed of the cyclist?

Thanks.

At 6 min from starting (bus A & B),
Distance of cyclist & Bus A from start point = 1000m/min x 6 min= 6000m

At 8 min from starting (bus A & B),
Distance of cyclist & Bus B from start point = 800m/min x 8 min= 6400m

In 2 min,
distance travelled by cyclist = 6400m-6000m = 400m
Cyclist's speed = 400m/2min = 200m/min

cheers.

[kwcllf]

MathIzzzFun:

kwcllf:

Hi, please help.


2 buses, A and B, travel from the same end of the road at the same time in the same direction. After travelling 6 minutes, Bus A overtakes a cyclist. 2 minutes later, Bus B overtakes the same cyclist. If A and B travel at an average speed of 1000m/min and 800m/min respectively, what is the average speed of the cyclist?

Thanks.

At 6 min from starting (bus A & B),
Distance of cyclist & Bus A from start point = 1000m/min x 6 min= 6000m

At 8 min from starting (bus A & B),
Distance of cyclist & Bus B from start point = 800m/min x 8 min= 6400m

In 2 min,
distance travelled by cyclist = 6400m-6000m = 400m
Cyclist's speed = 400m/2min = 200m/min

cheers.

Thanks! you made it look so easy :salute:

[Winx5015]

Hi please help me to solve this question.


Mr Lim had some red and green beads. 60% of his beads were red and the rest were green. He lost some of his red beads and the percentage of the beads which were red decreased by 40%. He then had 760 red and green beads left. How many red beads did he lose?

Thanks.

[underthesea]

This is dd’s prelim question.


Mrs B used either 4 red buttons or 2 blue buttons to make each dress. The total number of dresses she made was 35. The total number of red buttons used was 74 more than the total number of red buttons used.

(a) how many red buttons were used altogether?
(b) how many blue buttons were used altogether?

Besides guess & check, any other method to solve this problem?

TIA.

[tianzhu]

Winx5015:

Hi please help me to solve this question.


Mr Lim had some red and green beads. 60% of his beads were red and the rest were green. He lost some of his red beads and the percentage of the beads which were red decreased by 40%. He then had 760 red and green beads left. How many red beads did he lose?

Thanks.

Hi

At first

Red ------ 60%

Green ------- 40%

He lost some of his red beads and the percentage of the beads which were red decreased by 40%.

60% * 60/100 ------- 36%

36 + 40 ------ 76

76% ------- 760

1% -------- 10

36% -------- 360 (number of red beads left)

Number of red beads at first -------- 60% ------- 600

Number or red beads lost ------- 600 – 360 ------- 240

Best wishes

[tianzhu]

underthesea:

This is dd's prelim question.


Mrs B used either 4 red buttons or 2 blue buttons to make each dress. The total number of dresses she made was 35. The total number of red buttons used was 74 more than the total number of red buttons used.

(a) how many red buttons were used altogether?
(b) how many blue buttons were used altogether?

Besides guess & check, any other method to solve this problem?

TIA.

Hi

Please check sentence highlighted in pink.

I think it should be read as

\"The total number of red buttons used was 74 more than the total number of blue buttons used.\"

GC is one possible way.You may also use \"Make a Supposition\"

Here's an earlier solution for a similar type of question, hope this helps.

For your question,the answers are 96 red buttons (24 dresses with red buttons) and 22 blue buttons (11 dresses with blue buttons).

Best wishes

http://farm8.staticflickr.com/7016/6828705773_53738730b6_z.jpg\">

[its888me]

Need help in 2 Questions, Nanyang Prelim 2010, Paper 2:


Q10:

Kingsley planned to cycle from Town P to Town Q. If he were to cycle at 10 km/h, he would reach Town Q at 7.45pm. If he were to cycle at 12 km/h, he would reach Town Q at 7.15pm. What was the distance between Town P and Town Q?

Q17:

TGhere were some blue marbles and white marbles in a bag. If 70 blue marbles were to be removed from the bag, the ratio of the number of blue marbles to the number of white marbles would be 3 : 4. If 112 white marbles were to be removed from the bag instead, the tatio of the number of blue marbles to the number of white marbles would be 8 : 7. When 48 more blue marbles were to be added into the bag, what percentage of all the marbles would be blue marbles?


TIA!

[Winx5015]

Thanks tianzhu for your help

[its888me]

its888me:

Need help in 2 Questions, Nanyang Prelim 2010, Paper 2:


Q10:

Kingsley planned to cycle from Town P to Town Q. If he were to cycle at 10 km/h, he would reach Town Q at 7.45pm. If he were to cycle at 12 km/h, he would reach Town Q at 7.15pm. What was the distance between Town P and Town Q?

Q17:

TGhere were some blue marbles and white marbles in a bag. If 70 blue marbles were to be removed from the bag, the ratio of the number of blue marbles to the number of white marbles would be 3 : 4. If 112 white marbles were to be removed from the bag instead, the tatio of the number of blue marbles to the number of white marbles would be 8 : 7. When 48 more blue marbles were to be added into the bag, what percentage of all the marbles would be blue marbles?


TIA!

Can someone help me with the 2 questions? Many thanks!

[tianzhu]

its888me:

Kingsley planned to cycle from Town P to Town Q. If he were to cycle at 10 km/h, he would reach Town Q at 7.45pm. If he were to cycle at 12 km/h, he would reach Town Q at 7.15pm. What was the distance between Town P and Town Q?

Hi

You may tackle this question in a few ways.

For Speed questions, it’s helpful to start with a simple diagram.

At 12 km/h, he would reach Town Q at 7.15pm.

If he were to cycle at 10 km/h, he would be (10*1/2) or 5 km away.

Difference in speed ------- 12 – 10 ------ 2

Time taken ------- 5/2 ------- 2.5 h

Distance between P and Q ------- 2.5*12 ------- 30 km

or alternatively (3*10) ------- 30 km.

Another way if students are familiar with inverse proportion.

Speed is inversely proportional to time (distance remains constant).When speed is higher, time taken is shorter.

Speed -------- 12:10 ------- 6:5

Time ------- 5:6

1 unit ------- 1/2h

5 units ------- 5*1/2 ------- 2.5

Distance between P and Q -------- 2.5*12 ------- 30 km

Another way, use common multiple.

A common multiple of 12 and 10 is 60.

Distance ------- Speed*Time

60/12 ------ 5h

60/10 ------ 6h

Difference -------- 1h

We want a difference of 1/2h, so reduce distance to 30km.

30/12 ------- 2.5h

30/10 -------- 3h

Difference ------- 0.5h or 1/2h

Best wishes