Q&A - PSLE Math

[ksmama]

[quote][/quote]

MathIzzzFun:

match3frog:

Please help with the following question:

Hi mathsizzfun,
Regardg yr ans to the foll questn, my kid calculated a diff way n the ans is different. Please comment on why his method is not acceptable. Is it because when d ques asks for average sp, we have to calculate based on whole dist n time taken n not assume aver sp same throughout? Thanks.

Diff in speed-> 65/3 =21.67km/h
Speed of car 70+21.67 = 91.67km/h.





A car was travelling from Town P to Town Q.

After completing 2/7 of the journey in 1/2 hour, the car passed a van travelling at a constant speed of 70km/h in the same direction.
3 hours later, the car reached Town Q but the van was still 65 km away from Town Q.

(a) Find the average speed of the car.

(b) If the van left Town P at 0810, at what time would it arrive at Town Q?

Thank you

5/7of distance PQ --> 3 x 70 + 65 = 275 km
distance PQ --> 275/5 x 7 --> 385 km
total time taken by car --> 3. 5 h
average speed of car --> 385/3. 5 --> 110 km/h

cheers.

[ksmama]

Sori my post somewh in the middle of incomplete quote. Pls bear with my mess n read thru

[jonaandr]

please help to solve the problem.


Mrs Hodge bought three times as many key chains as stuffed toys and spent $124 in total. She spent $64 more on the stuffed toys than the key chains. Given that a stuffed toy cost $8.40 more than a key chain, find the cost of a key chain.

Thanks a lot!

[tianzhu]

jonaandr:

please help to solve the problem.


Mrs Hodge bought three times as many key chains as stuffed toys and spent $124 in total. She spent $64 more on the stuffed toys than the key chains. Given that a stuffed toy cost $8.40 more than a key chain, find the cost of a key chain.

Thanks a lot!

Hi

A neat way is to use MD.Due to time constraints, I shall give you only some pointers.

Amount@stuffed toys ------- 94

Amount@key chains ------- 30

Draw 3 boxes to show number of key chains.

Draw 1 box to show number of stuffed toys.

Cost of 1 unit of key chains -------30/3 ------- 10

Cost of 1 unit of key chains -------94

94 – 10 ------ 84

This extra $84 is due to the number of stuffed toys costing $8.40 more than a key chain.

Number of stuffed toys ------ 84/8.4 ------- 10

Number of key chains ------- 30

Cost per key chain ------- 30/30 ------- 1

Best wishes

[cimman]

brastilava:

Hi, please help in these 2 questions:


2) I am a 2-digit number. I am a multiple of 4. When I am divided by 9, there will be a remainder of 6. When I am divided by 7, there will be a remainder of 5. Who am I?

some terminology foundation first:
http://i45.tinypic.com/21oas2d.png\">

coming up with the equation:
http://i49.tinypic.com/dev04m.png\">

plugging in the numbers:
http://i48.tinypic.com/1zlsm88.png\">

[rajamalar]

hi thank you for your method it is fambous

[cimman]

rajamalar:

hi thank you for your method it is fambous

you're welcome.

[imacsg]

At 9am Jerome left P Town for Y Town which was 540 km away. 2 hours later, Michael left P town for Y Town. He travelled at an average speed of 40 km/h faster than Jerome and overtook him at 3 pm.

a) What was Jerome’s average speed?
b) How far was Jerome from Y town when Michael reached his destination?

Can anyone help the above question? Thanks.

[MathIzzzFun]

imacsg:

At 9am Jerome left P Town for Y Town which was 540 km away. 2 hours later, Michael left P town for Y Town. He travelled at an average speed of 40 km/h faster than Jerome and overtook him at 3 pm.

a) What was Jerome's average speed?
b) How far was Jerome from Y town when Michael reached his destination?

Can anyone help the above question? Thanks.

Michael left Town P at 11 am and overtook Jerome at 3 pm ie 4 h later
40 km/h x 4h = 160 km --> Michael travelled 160km more than Jerome in 4h -- this is the \"catch up\" distance which is the distance travelled by Jerome from 9am to 11 am (2h)
Jerome's speed = 160 km/2 h = 80 km/h

alternatively, we can also use time ratio/speed ratio
When they meet,
time taken by Michael --> 11 am to 3 pm --> 4h
time taken by Jerome --> 9 am to 3pm --> 6h
Speed ratio of Michael : Jerome = 6 : 4 --> 3u : 2u
1u --> 40km/h, Jerome's speed --> 2 x 40 km/h = 80 km/h

with this, I think you can work out part (b)


cheers.

[AJH]

tianzhu:

AJH:

Hi - how did u get 480? I got 460. Thank u.

Hi

This question is crafted in such a way that it’s neat to use MD.

You may also use Units and Parts or letters of the alphabet to show the variables.

What you are seeing now is already the MD.The boxes are labelled with units and parts to enable students using the UP to see better.

The number “480” refers to the number of girls.

Best wishes

:thankyou: for your help. But isn't 30% of students in the parade ground and 70% of students at the indoor sports hall = 180 + 280 = 460?