Q&A - PSLE Math

[tianzhu]

peggy:

Please help with some speed questions here.


1. At 9.30am, Train One which was 200m long, pulled out of Station X and traveled towards Station Y at a uniform speed of 80km/h. Half an hour later, Train Two which was 150m long, left Town Y and traveled towards Town X at a uniform speed of 90 km/h.
A) How far Train One traveled when Train Two left Station Y?
B) The two trains met each other of the tunnel. Calculate the length of the tunnel.

Hi

I think some information is missing here.

Best wishes

[Winx5015]

Hi tianzhu,


thanks for your help.

Have a wonderful weekends

[peggy]

Hi Tianzhu,


Sorry, here’s the info.

B) the two trains met each each in a tunnel. Both trains took 15mins to completely come out of the tunnel. Calculate the length of the tunnel.

Thank you.

[tianzhu]

peggy:

Hi Tianzhu,


Sorry, here's the info.

B) the two trains met each each in a tunnel. Both trains took 15mins to completely come out of the tunnel. Calculate the length of the tunnel.

Thank you.

Hi

Speed = Distance *Time

a) Train A = ½*80 = 40

b)Train A = ¼*80 = 20
Train B = ¼*90 = 22.5

Length of tunnel = (20+22.5) – 0.2 - 0.15 = 42.15km

Best wishes

[tianzhu]

Hi peggy


Where are your Q2 and Q3 from?

Q2)
As in any questions on Speed, it’s always useful to draw a time/distance line.

Alvin ------ Town P to Town Q
Simon ------ Town Q to Town P

For Simon, distance covered in 2h ------- 2*80 ------- 160km
160 + 40 ------- 200

Total time taken by Alvin ------ 6h (7am-1pm)
6 - 2 ------ 4

Alvin travelled 200km in 4h (7am-11am), hence his speed ------ 200/4 ------- 50km/h

2*50 ------- 100km
100/80 ------ 1.25 h

Simon ------- start @ 0945h from Town Q.

Q3)
In 1h the truck is faster than the van by 20km
In 6h the truck travels 120km more than the van.

Distance travelled by the van -------- 80 + 1 unit (distance travelled by the van in 6h)
Distance travelled by the truck ------- 1 unit + 120.

1 unit + 80 ------- 90%
1 unit + 120 ------- 100%

10% ------ 120 – 80 ------ 40
100% ------- 400

Distance between Town A and Town B ------- 400km

Speed of lorry ------ 400/6 ------- 66 2/3 km/h

Best wishes

[Zack7]

Hello in general, ratio problems are best approached by thinking in terms of fractions or models or algebra.


1) let the bigger number be x, smaller number be y

X+y = 5
X-y= 1

Solving, y=2, x =3
Now,
Xy = 24

This means there is a scaling of 4 . Since 2x3 is only 6. So to get 24, we scale the x and y values by 4. Remember that we are dealing with ratios.

So the bigger number is 12, the smaller is 8.




2) again, to simplify, just take it as 4 markers and 3 files were bought.

It cost 2 dollars for 4 markers, 1 dollar for 3 files.

This means 1marker cost 50cents and 1 file cost 33.3cents

1/2 : 1/3 is 3:2

[Bunny27]

tianzhu:

Hi peggy


Where are your Q2 and Q3 from?

Q2)
As in any questions on Speed, it’s always useful to draw a time/distance line.

Alvin ------ Town P to Town Q
Simon ------ Town Q to Town P

For Simon, distance covered in 2h ------- 2*80 ------- 160km
160 + 40 ------- 200

Total time taken by Alvin ------ 6h (7am-1pm)
6 - 2 ------ 4

Alvin travelled 200km in 4h (7am-11am), hence his speed ------ 200/4 ------- 50km/h

2*50 ------- 100km
100/80 ------ 1.25 h

Simon ------- start @ 0945h from Town Q.

Q3)
In 1h the truck is faster than the van by 20km
In 6h the truck travels 120km more than the van.

Distance travelled by the van -------- 80 + 1 unit (distance travelled by the van in 6h)
Distance travelled by the truck ------- 1 unit + 120.

1 unit + 80 ------- 90%
1 unit + 120 ------- 100%

10% ------ 120 – 80 ------ 40
100% ------- 400

Distance between Town A and Town B ------- 400km

Speed of lorry ------ 400/6 ------- 66 2/3 km/h

Best wishes

Hi, can someone help on this question:

1. At a carnival, 30% of the people are adults, 20% are girls and the rest are boys. After some adults have left, the percentage of adults at the carnival becomes 20%. How many adults have left the carnival?

:thankyou:

[Chenonceau]

My Question 1

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Please help... Thank you.

[Chenonceau]

My Question 2

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Thank you!

[tianzhu]

Chenonceau:

My Question 2

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Thank you!

Hi

Good Morning.

Hope this helps.

Best wishes.

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