Q&A - PSLE Math
-
Need help on this?
4 children decide to weigh themselves 3 at a time. Only 4 different readings were repeatedly recorded:
99.5kg, 108.1kg, 111.7kg and 116.3kg.
Find the total mass of the heaviest and lightest child?
Ans: 74.6kg -
Hi Charsen
Thank you for the pointers. Thats another good method that you have helped me to see.
Cheers… -
Nan Hua prelim 2011, Q15.
A car left Town A at 0800 and travelled to Town B at an average speed of 60 km/h. At the same time, a lorry left Town B for Town A. At 1130, the car and the lorry were 85km apart after passing each other eralier. If the car arrived at Town B at 1300, at what time would the lorry arrive at Town A?
Answer is 1400, but seems that it’s not right.
TIA! -
Hi Hi,
Need some guide on these two questions, thanks in advance
1) Andy can dig a hole in 3 hours.
Peter can dig a similar hole in 2 hours.
Roslan can dig a similar hole in 6 hours.
Fariq can dig a similar hole in 4 hours.
If they all worked together at their own speed, how long would it take to dig a hole?
2) There were 1200 peope in Room A and Room B. 30% of the 800 people in Room A were women. 40% of the people in Room B were men. After some people in both rooms had changed rooms, 25% of the people in Room A and 75% of the people in Room B were women. How many people were there in Room A after the change? -
its888me:
HiNan Hua prelim 2011, Q15.
A car left Town A at 0800 and travelled to Town B at an average speed of 60 km/h. At the same time, a lorry left Town B for Town A. At 1130, the car and the lorry were 85km apart after passing each other eralier. If the car arrived at Town B at 1300, at what time would the lorry arrive at Town A?
Answer is 1400, but seems that it's not right.
TIA!
This question has been discussed before.
It’s useful to have a pictorial representation for Speed questions.
I’ll just provide some pointers.
Draw a bar, and label A and B at both ends.
At 1130, the car is at point C and the lorry is at point D.(D is nearer to A).
From 0800 to 1130, the car covered 60*3.5 ----- 210 km (A to C)
From 1130 to 1300, the car covered 60*1.5 ----- 90 km (C to B)
Distance (B to D) travelled by lorry from 0800 to 1130 ------ 90 + 85 ------ 175 km
From here, lorry’s speed ------ 175/3.5 ------- 50 km/h
From point D to A, the lorry covered (210 – 85) which is 125 km
Time taken by lorry ------125/50 ------ 2.5 h
From 1130h, add 2.5h, this gives 1400 h
Best wishes -
dicoyote:
Hi
1) Andy can dig a hole in 3 hours.
Peter can dig a similar hole in 2 hours.
Roslan can dig a similar hole in 6 hours.
Fariq can dig a similar hole in 4 hours.
If they all worked together at their own speed, how long would it take to dig a hole?
One possible way, use common multiple.
A common multiple of 3,2,6 and 4 is 12.
Number of units required to dig a hole ------ 12
Andy ------ 4 units (12/3)
Peter ------ 6 units
Roslan ------ 2 units
Fariq ------ 3 units
4+6+2+3 ------- 15 units (If they all worked together at their own speed)
Time taken ------- 12/15*60 ------ 48 minutes
Best wishes -
dicoyote:
Q2.Hi Hi,
Need some guide on these two questions, thanks in advance
2) There were 1200 peope in Room A and Room B. 30% of the 800 people in Room A were women. 40% of the people in Room B were men. After some people in both rooms had changed rooms, 25% of the people in Room A and 75% of the people in Room B were women. How many people were there in Room A after the change?
here are some similar questions that may help:
http://www.flickr.com/photos/62167097@N02/6858744276/in/set-72157629537287046/
http://www.flickr.com/photos/62167097@N02/7080366811/in/set-72157629537287046
cheers. -
dicoyote:
Q1...Hi Hi,
Need some guide on these two questions, thanks in advance
1) Andy can dig a hole in 3 hours.
Peter can dig a similar hole in 2 hours.
Roslan can dig a similar hole in 6 hours.
Fariq can dig a similar hole in 4 hours.
If they all worked together at their own speed, how long would it take to dig a hole?
In 12 hours,
Andy --> 4 holes
Peter --> 6 holes
Roslan --> 2 holes
Fariq --> 3 holes
Total :
Andy+Peter+Roslan+Fariq
--> 15 holes in 12 hours
--> 1 hole in 12/15 h or 48 min
cheers. -
Chan09:
add the 4 sets of readings (A+B+C, A+B+D, A+C+D, B+C+D) to get 3 sets of A+B+C+D, you can then find the individual mass.Need help on this?
4 children decide to weigh themselves 3 at a time. Only 4 different readings were repeatedly recorded:
99.5kg, 108.1kg, 111.7kg and 116.3kg.
Find the total mass of the heaviest and lightest child?
Ans: 74.6kg
cheers. -
its888me:
HiNan Hua prelim 2011, Q15.
A car left Town A at 0800 and travelled to Town B at an average speed of 60 km/h. At the same time, a lorry left Town B for Town A. At 1130, the car and the lorry were 85km apart after passing each other eralier. If the car arrived at Town B at 1300, at what time would the lorry arrive at Town A?
Answer is 1400, but seems that it's not right.
TIA!
1400 is correct.
at 1130,
Distance of car from Town B --> 1.5h x 60 km/h = 90km
In 3.5h (0800-1130),
distance travelled by lorry --> 90km + 85km = 175 km
Lorry's speed = 175 /3.5 km/h = 50 km/h
Total time taken for Car to travel from Town A to Town B = 5h (from 0800 to 1300)
Total time taken for lorry from B to A = 60/50 x 5 = 6 hours
0800 + 6 hours --> 1400
cheers.
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