Q&A - PSLE Math

[david59]

MathIzzzFun:

match3frog:

Please help with the following question:


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.

Hi all,
I am inclined to say that the qn is flawed.
If the car's speed is 110km/hr, then in three hours after passing the van and reaching town Q, he would have travelled 330km. However, you rightly calculated that the distance between the point where the car passed the van and town Q is 275km. So, there is a discrepency here.
I suspect the fraction used in the qn is unneccessary. It should have just been \" After travelling for 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\".

[fantasy1]

Hi Tian Zhu and Charsen for the help in solving the previous qns.


I have 1 more qn that needs help:
1)Sarah had 10 more 50cent coins than $1 coins. After she exchanged all the 50cent coins for $1 coins, she had 65 $1 coins altogether.How many $1 coins did she have at first ?


Thank You

[MathIzzzFun]

david59:

MathIzzzFun:

[quote=\"match3frog\"]Please help with the following question:


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.

Hi all,
I am inclined to say that the qn is flawed.
If the car's speed is 110km/hr, then in three hours after passing the van and reaching town Q, he would have travelled 330km. However, you rightly calculated that the distance between the point where the car passed the van and town Q is 275km. So, there is a discrepency here.
I suspect the fraction used in the qn is unneccessary. It should have just been \" After travelling for 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\".[/quote]Average speed for whole journey does not mean the car travelled at constant speed of 110 km/h throughout.

In this case, for the first 2/7 of the journey, the car's average speed is 220 km/h and for the final 5/7 of the journey, the car's average speed is 91 2/3 km/h

cheers.

[MathIzzzFun]

fantasy1:

Hi Tian Zhu and Charsen for the help in solving the previous qns.


I have 1 more qn that needs help:
1)Sarah had 10 more 50cent coins than $1 coins. After she exchanged all the 50cent coins for $1 coins, she had 65 $1 coins altogether.How many $1 coins did she have at first ?


Thank You

total amount --> $65
10 more 50 cent coins --> remove the 10 50-cent coins and there will be equal number of 50-cent and $1 coins with total value = $65 - 10 x $0.50 = $60

For every set of 1x$1 coin + 1x$0.50, value --> $1.50
$60/$1.50 = 40 sets -- 40 each of 50-cent and $1
total number of 50-cent coins --> 40+10 = 50
total number of $1 coins --> 40

cheers.

[i_am_not_a_parent]

rsorchid:

Thanks so much.

tianzhu:

[quote=\"rsorchid\"]Pls help, Thanks.

A florist had some roses, tulips and carnations. After selling some of them, there were 6 tulips for every 5 roses and 7 roses for every 3 carnations. After selling 168 roses, she had 456 tulips and carnations left. The number of tulips sold was the same as the number of carnations sold.
a) How many roses had she at first?
b) If the number of tulips was twice the number of carnations at first, what is the total number of tulips and carnations sold?

Hi

A neat way is to use MD.

T:R ------ 6:5 -------42:35

R:C ------ 7:3 -------- 35:15

Since the share for roses is repeated, make it the same for both set of ratios

15 + 42 ------ 57

57 units -------- 456

1 unit ------- 8

(a)Number of roses left ------- 35*8 -------- 280

Number of roses@first -------- 280+168 -------- 448

(b) Draw 1 box to show number of tulips/carnation sold.

Number of tulips left ------- 42*8 -------- 336

Number of carnations left -------- 120

1 box + 336 ------- 1 box + 120 = 1 box + 120

1 box ------- 96

The total number of tulips and carnations sold ------- 96*2 ------- 192

Best wishes

[/quote]I dun under stand the part that is highlighted in red.. I appreciate ur help

[i_am_not_a_parent]

rsorchid:

Thanks so much.

tianzhu:

[quote=\"rsorchid\"]Pls help, Thanks.

A florist had some roses, tulips and carnations. After selling some of them, there were 6 tulips for every 5 roses and 7 roses for every 3 carnations. After selling 168 roses, she had 456 tulips and carnations left. The number of tulips sold was the same as the number of carnations sold.
a) How many roses had she at first?
b) If the number of tulips was twice the number of carnations at first, what is the total number of tulips and carnations sold?

Hi

A neat way is to use MD.

T:R ------ 6:5 -------42:35

R:C ------ 7:3 -------- 35:15

Since the share for roses is repeated, make it the same for both set of ratios

15 + 42 ------ 57

57 units -------- 456

1 unit ------- 8

(a)Number of roses left ------- 35*8 -------- 280

Number of roses@first -------- 280+168 -------- 448

(b) Draw 1 box to show number of tulips/carnation sold.

Number of tulips left ------- 42*8 -------- 336

Number of carnations left -------- 120

1 box + 336 ------- 1 box + 120 = 1 box + 120

1 box ------- 96

The total number of tulips and carnations sold ------- 96*2 ------- 192

Best wishes

[/quote]I dun understand the part that is highlighted in red.. I appreciate ur help

[fantasy1]

Hi MathIzzzFun,


Thank you for yr help

[david59]

MathIzzzFun:

david59:

[quote=\"MathIzzzFun\"]Hi all,

I am inclined to say that the qn is flawed.
If the car's speed is 110km/hr, then in three hours after passing the van and reaching town Q, he would have travelled 330km. However, you rightly calculated that the distance between the point where the car passed the van and town Q is 275km. So, there is a discrepency here.
I suspect the fraction used in the qn is unneccessary. It should have just been \" After travelling for 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\".

Average speed for whole journey does not mean the car travelled at constant speed of 110 km/h throughout.

In this case, for the first 2/7 of the journey, the car's average speed is 220 km/h and for the final 5/7 of the journey, the car's average speed is 91 2/3 km/h

cheers.

[/quote]Looks like the car was racing at extreme speed of 220km/hr in the GrandPrix F1 for half an hour and then suddenly found himself chasing past a van and so slowed down to a crawl at only 91 2/3 km/hr.
This qn is unacceptable for a child to do though technically speaking is not wrong. He would find the first half hr speed too incredible and so doubt his own working.
Good nite!

[tianzhu]

Essential:

Hi Tian Zhu thank you for your help for earlier question. One more question from Nanyang Prelim 2012. Q13. both shops. ABC and XYZ , offered a 15% discount for the same type of mattress. If Mr Muthu were to buy from shop XYZ ,he would have paid $38.25 less than the discounted price in shop ABC. a) What was the discounted price in the shop ABC ?

b) the original price of the mattress in Shop ABC was $1510. what was the minimum percentage discount it must offer so that the discounted price in shop ABC would be lower than the discounted price in Shop XYZ? Give your answer connect to the nearest percent.Thankyou in adv

Hi

15% ------- 38.25

100% ------- 255 (original price in XYZ)

For ABC ------ 255*100/85 ------- 300

a) Difference -------300 – 255 ------- 45

For (b)

Discounted price in ABC -------- 1510*0.85 ------ 1283.50

Discounted price in XYZ -------- 1283.50 – 38.25 ------- 1245.25

1510 – 1425.25 ------- 264.75

264.75/1510*100% ------- 18%

Best wishes

[zanen]

tianzhu:

zanen:

help ls Two cars race around a circular track at constant speeds starting at the same point. If they travel in opposite directions, then they meet every 30 seconds. If they travel in the same direction, then they meet every two minutes. If the track is 1800m long,what is the speed of each car?

Hi

Could you share with us where you take this question from?

Is this a PSLE type of question?

The answers to your question are 22.5m/s and 37.5m/s.

please help me. it was given by the relief teacher from my math teacher. the relief teacher dont know how to teach math ask me to find out by myself//
Best wishes