Q&A - PSLE Math

[MathIzzzFun]

small:

Hi,


My mind is block and I got 2 answer for this question. :stupid:

Please help and thanks in advance.
[quote]The spped of a car was 60 km/h abd the speed of a van was 45 km/h. They started from Town P at the same time and travelled along the same route towards Town Q. The car reached Town Q 1 hour 40 min earlier than the van. What was the distance travelled by the can when the car reached Town Q?

[/quote]Hi

Time ratio, Car : Van --> 45 : 60 = 3u : 4u
1u --> 1h 40 min = 100min, 3u --> 300 min
distance travelled by Van when the car reach town
= 300 min x 45 km/h
= 225 km

cheers.

[small]

Good morning Tianzhu and MathIzzzFun,


Thanks a lot.

I was using algebra method which came out 2 different answers, 225km and 300km..

p/s: Tianzhu got an eagle eyes, so sharp..

[jarenchuatw]

Yup, 100% correct. But had problem explaining to my son, he could not comprehend why I need to add 8 secs and not 12 seconds. Whew, it took a while before he got the picture. Tks!

[tianzhu]

Winx5015:

Using make a list method
Q1). Mother had less than 3105 coins. If she put them equally into boxes of 24 or 36, she would have 15 coins left. How many boxes did she have if she arranged the coins into boxes of 30?

Hi

Your teacher requested students to use “Make a list”. Perhaps, he/she wanted to keep the students occupied.

Don’t lose marks over this type of questions. It may be tedious but as long as students do their listing meticulously, the marks should be safe.

Do the listing preferably with a tabulated list of the multiples of 24 and 36 plus 15.

The answer is 3039.

The number of boxes is 102.

Best wishes

[tianzhu]

Winx5015:

Using restating problem
Q2). 3 similar tables and 4 similar chairs cost $240. 2 such tables and 3 similar racks cost $115. 1 such chair and 2 such racks cost $95. How much do 2 such tables and 1 such chair cost altogether?

Hi

3T + 4C ------ 240
2T + 3R ------ 115
1C + 2R ------ 95

5T + 5C + 5R ------- 450 (240+115+95)

1T + 1C + 1R ------- 90
(x2)
2T + 2C + 2R ------- 180

1C + 2R ------ 95

Therefore, 2T + 1C ------ 180 – 95 ------85

Best wishes

[peggy]

Please help with this question. Thanks in advance.


Ben cycles from his home to the church every Sunday. If he were to cycle at 10km/h, he would reach the church at 3pm. If he were to cycle at 15km/h, he will reach there at 1pm. a) how far does Ben have to cycle from his home to the church? b) at what average speed must he cycle if he wants to reach the church at 2pm?

[tianzhu]

peggy:

Please help with this question. Thanks in advance.


Ben cycles from his home to the church every Sunday. If he were to cycle at 10km/h, he would reach the church at 3pm. If he were to cycle at 15km/h, he will reach there at 1pm. a) how far does Ben have to cycle from his home to the church? b) at what average speed must he cycle if he wants to reach the church at 2pm?

Hi

There are a few ways to solve this question.

One way is to use inverse proportion.

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

Speed ----- 2:3 (10:15)
Time ------- 3:2

1 unit ------ 2h (1pm and 3pm)

2 units ------ 4h
Distance ------- 15*4 ------- 60km

Alternatively
3 units ------ 6h
Distance ------ 10*6 ------ 60km

If he wants to reach the church@2pm

Time taken ------5h

60/5 ------ 12km/h

Best wishes

[peggy]

Tianzhu,


Thank you so much for your quick reply.

All the best!

Peggy

[JGMum]

jarenchuatw:

Yup, 100% correct. But had problem explaining to my son, he could not comprehend why I need to add 8 secs and not 12 seconds. Whew, it took a while before he got the picture. Tks!

That's great, thanks for the feedback!

[Winx5015]

Hi tianzhu,


thanks for your solution.

Good nite