Dear David59, you might want to consider another method to solve the question below:-
1) Gerald had 60 sweets more than Herlina. After eating half of what they had, the ratio of the number of Gerald’s sweets to the number of Herlina’s sweets became 3:2.
a) How many sweets did Gerald eat?
b) Gerald gave Herlina some sweets and the ratio became 8:7. How many sweets did Gerald give Herlina?
If Gerald has 60 sweets more than Herlina, after both of them have eaten half of what they have, Gerald will have 30 sweets more than Herlina.
Since the ratio then becomes 3:2, we can deduce that 1 unit = 30 sweets.
i.e. (a) Gerald has 90 sweets; Herlina has 60 sweets.
(b) since the ratio becomes 8:7, we can deduce Gerald has given 10 sweets to Herlina, i.e. Gerald has 80 sweets, Herlina has 70 sweets.
The model approach is fine but if students can grasp this concept, this method will save them some time.
Good to learn this concept and be aware because it can be used in several other types of problem sums as well including speed questions.
Basically, two steps:-
(a) first, recognise that the difference between A & B becomes half when both A & B are reduced by half, i.e. if A is 100 more than B, when A & B are reduced by half, then A becomes 50 more than B.
(b) and if the question then state that the ratio becomes e.g. 5:3, then we know straight away that 2 units = 50.
Hope this helps.
Best Regards,
iCreative Math
Posts made by iCreative Math
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RE: Q&A - PSLE Math
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RE: Q&A - PSLE Math
A and B has some sweet. If A eat 2 a day, and B eat 1 a day - A will have 68 left while B has none. If A eat 1 a day and B eat 2 a day - A will have 122 left while B has none. How many sweet do they have at first?
The answer is A has 140 sweets and B has 36 sweets at first.
I have coincidentally recorded two YouTube videos recently explaining a similar question. The questions have different figures but the concept tested and hence the problem-solving method is identical.
You might want to get your child to view the YouTube videos.
I have recorded two different videos, one using the \"normal\" method and another using the \"Guess & Check\" method.
The generic simplified problem-solving methods taught in the videos will apply to all similar questions of this nature.
Hope it is helpful.
Best Regards
iCreative Math
YouTube Lesson Videos:
http://www.youtube.com/watch?v=JXpXuz2Tqf4 (PSLE “Double-IF” Question)
http://www.youtube.com/watch?v=jcU2hv-GTBE (PSLE “Double-IF” Question using “Guess & Check” Method) -
RE: Q&A - PSLE Math
Yum Yum, your question below:-
1) Mary bought some red marbles and have half to Noel.
Noel bought some blue marbles and gave half to Mary.
Mary lost 16 red marbles and Noel lost 55 blue marbles.
The ratio of Mary's red marbles to blue marbles became 18:85 and the ratio of Noel's red marbles to blue marbles became 7:20.
How many red marbles did Mary buy?
is adapted from the 2009 PSLE question with changes to the numbers and the resultant ratios but they are essentially similar questions.
I have posted the explanation of the solution to the 2009 PSLE question in YouTube (see the link below).
I hope the verbal explanation will be helpful for your child to understand the solution to this sort of questions.
http://www.youtube.com/watch?v=epaXFwd5j_0
Best Regards,
iCreative Math -
RE: Q&A - PSLE Math
Suz855,
I believe you are correct in both instances.
For Q1, the answers, based on the facts in the question, are 30 km/hr for the speed of the car, and 10 km/hr for the speed of the lorry. Agree with you that both the speeds are not very realistic.
For Q2, the question is indeed incomplete. Based on the facts given, there are many possibilities. For example, if the distance between the two towns is 380 km, the average speed of Mr R would be 40 km/hr. If the distance is 460 km, then the average speed of Mr R would be 30 km/hr.
Best Regards,
iCreative Math -
RE: Q&A - PSLE Math
Radius of small wheel = 7 cm
Radius of big wheel = 21 cm (given ratio of 1:3)
In one complete revolution each, the small and big wheels would have travelled a combined distance of 2 X 3.14 X 28 = 175.84
For the centre to be 113 cm apart, the total distance travelled would have to be 641 - 113 = 528 cm.
The wheel would have each make 528 / 175.84 = 3 complete revolutions each.
Regards.
iCreative Math -
RE: Q&A - PSLE Math
most welcome, mathnoonbs … keeping sending your questions … glad to share my methods particularly for challenging questions … i pity the 12 years old … P6 questions are so varied and hence more challenging … they need simplified structured models to help them re-produce the solutions under examination conditions.
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RE: Q&A - PSLE Math
Never easy to explain Math solution via writing without verbal explanation.
The question mentioned that after taking away 16 50-cents coins, and adding the same value in 20-cents coins (which is 40 20-cents coins), the number of 50-cents coins left in the box is 7/8 of the number of 20-cents coins.
Hence, we deduce that the ratio of 20-cents coins to 50-cents coins is 8:7.
Therefore,
20-cents coins : 50-cents coins is 8 units : 7 units
or (8-units + 40) : (7 units + 35)
We introduce the 40 because we know 40 coins was added.
The number of 20-cents coins At First is therefore 8 units.
If we add 40 coins to the ratio for 20-cents coins, we need to add 35 to the number of 50-cents coins to maintain the ratio of 8:7.
I hope this further explanation is clear.