Dear Parents,
If you have any Math questions, please feel free to post here. I will get back as soon as possible. I will also post common exam questions weekly so do check out my post frequently.
1) Concept: External unchanged (Ratio)
On a train, the ratio of the male to the number of female passengers was 5:9. After 20 female alighted, the ratio became 1:3. How many female passengers were there on the train at first?
Note: The number of male passengers remained unchanged. Only female passengers alighted.
Before > 5:9
After > 1:3 = 3:9 (muliply by 3 to make both male units the same)
Now we can compare the female units, notice there was a decrease from 5 units to 3 units (difference of 2 units)
Thus, the 2 units equates to the 20 female passengers.
2 units > 20
5 units > 50
There are 50 female passengers on the train at first.
Pri School Exam Hub
Discussions on tuition centres/enrichment services that specialise in Mathematics.

Adele Yeo  OrangeBelt
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Re: Pri School Exam Hub
by Adele Yeo » Tue Jun 25, 2013 8:33 pm
2) Concept: Constant difference (Ratio)
The ratio of Martin's age to Jeremy's age is 1:4. In 15 years time, the new ratio is 2:3. How old is Martin now?
Note: The age difference/ age gap always remain the same.
Thus, we have to make both difference the same.
1:4 (difference is 3 units)
2:3 = 6:9 (multiply by 3 to have the difference of 3 units)
Difference:
Martin: 1 unit to 6 units (Diff: 5u)
Jeremy: 4 units to 9 units (Diff: 5u)
Thus, the 5 units will be the growth of 15 years
5 units => 15
1 unit => 3
Martin is 3 years old now.
The ratio of Martin's age to Jeremy's age is 1:4. In 15 years time, the new ratio is 2:3. How old is Martin now?
Note: The age difference/ age gap always remain the same.
Thus, we have to make both difference the same.
1:4 (difference is 3 units)
2:3 = 6:9 (multiply by 3 to have the difference of 3 units)
Difference:
Martin: 1 unit to 6 units (Diff: 5u)
Jeremy: 4 units to 9 units (Diff: 5u)
Thus, the 5 units will be the growth of 15 years
5 units => 15
1 unit => 3
Martin is 3 years old now.

Adele Yeo  OrangeBelt
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Re: Pri School Exam Hub
by jwxh » Wed Jun 26, 2013 10:49 am
besides guess and check, what is the shortcut solution for below question. tks
A stapler cost $8. A dictionary cost $12.50. Tom bought 9 staplers and dictionaries. He paid $31 more for the staplers than the dictionaries. How many dictionaries did tom buy?
A stapler cost $8. A dictionary cost $12.50. Tom bought 9 staplers and dictionaries. He paid $31 more for the staplers than the dictionaries. How many dictionaries did tom buy?

jwxh  GreenBelt
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Re: Pri School Exam Hub
by Adele Yeo » Mon Jul 01, 2013 11:27 pm
Hi jwxh,
Thank you for the qn. I welcome more questions =)
A stapler cost $8. A dictionary cost $12.50. Tom bought 9 staplers and dictionaries. He paid $31 more for the staplers than the dictionaries. How many dictionaries did tom buy?[/quote]
Method 1: Algebra
Let the number of stapler be x. Let the number of dictionary be y.
Equation 1: x + y =9
Equation 2: 8x  12.5y = 31
From eqn 1, we can say that x = 9  y
Then we substitute x = 9  y into eqn 2.
8 (9  y)  12.5y = 31
72  8y  12.5y = 31
12.5y + 8y = 72  31
20.5y = 41
y = 2
Thus, he bought two dictionaries.
Method 2: Assumption method
Assume that Tom has spent all his money on staplers
9 x $8 = $72
Take out the $31 more that he spent on staplers
$72  $31 = $41
Now we can add up the amount of a stapler and a dictionary
$12.50 + $8 = $20.50 (1 set of stapler and dictionary)
Divide
$41 / $20.50 = 2
Thus, he bought two dictionaries.
EXAM TIPS: If you have time, you can check the answer.
Dictionary: 2 x $12.50 = $25
Staplers: 7 x 8 = $56
Difference: $56  $25 = $31
Thank you for the qn. I welcome more questions =)
A stapler cost $8. A dictionary cost $12.50. Tom bought 9 staplers and dictionaries. He paid $31 more for the staplers than the dictionaries. How many dictionaries did tom buy?[/quote]
Method 1: Algebra
Let the number of stapler be x. Let the number of dictionary be y.
Equation 1: x + y =9
Equation 2: 8x  12.5y = 31
From eqn 1, we can say that x = 9  y
Then we substitute x = 9  y into eqn 2.
8 (9  y)  12.5y = 31
72  8y  12.5y = 31
12.5y + 8y = 72  31
20.5y = 41
y = 2
Thus, he bought two dictionaries.
Method 2: Assumption method
Assume that Tom has spent all his money on staplers
9 x $8 = $72
Take out the $31 more that he spent on staplers
$72  $31 = $41
Now we can add up the amount of a stapler and a dictionary
$12.50 + $8 = $20.50 (1 set of stapler and dictionary)
Divide
$41 / $20.50 = 2
Thus, he bought two dictionaries.
EXAM TIPS: If you have time, you can check the answer.
Dictionary: 2 x $12.50 = $25
Staplers: 7 x 8 = $56
Difference: $56  $25 = $31

Adele Yeo  OrangeBelt
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Re: Pri School Exam Hub
by Adele Yeo » Mon Jul 01, 2013 11:41 pm
Concept: Repeated Identity
Mary and Jenny had a number of stickers in the ratio 4: 1. Jenny and Grace had a number of stickers in the ratio 2: 3. If they have a total of 169 stickers altogether, how many stickers does Mary have?
Exam tips!!
1. Highlight the key words
2. Identify the concept: Repeated identity
3. Write down the info provided in the question
Whose name is repeated twice? JENNY!!
M : J
4 : 1 (multiply by 2 to make Jenny's ratio the same)
J : G
2 : 3
Put the ratio together to compare
M : J : G
8 : 2 : 3
Total units = 8 + 2 + 3 = 13
13 units > 169 stickers
1 unit > 13 stickers
8 units > 104 stickers
Mary has 104 stickers
** Repeated identity questions can be in the form of percentages, fractions and ratio.
Mary and Jenny had a number of stickers in the ratio 4: 1. Jenny and Grace had a number of stickers in the ratio 2: 3. If they have a total of 169 stickers altogether, how many stickers does Mary have?
Exam tips!!
1. Highlight the key words
2. Identify the concept: Repeated identity
3. Write down the info provided in the question
Whose name is repeated twice? JENNY!!
M : J
4 : 1 (multiply by 2 to make Jenny's ratio the same)
J : G
2 : 3
Put the ratio together to compare
M : J : G
8 : 2 : 3
Total units = 8 + 2 + 3 = 13
13 units > 169 stickers
1 unit > 13 stickers
8 units > 104 stickers
Mary has 104 stickers
** Repeated identity questions can be in the form of percentages, fractions and ratio.

Adele Yeo  OrangeBelt
 Posts: 38
 Joined: Tue Jan 31, 2012 1:08 pm
 Total Likes: 0
Re: Pri School Exam Hub
by Adele Yeo » Thu Jan 29, 2015 3:02 pm
CHEWY MATH TUITION CENTRE
Unleash Their Potential!
Chewy Math is founded in October 2014. We believe in the potential in every child to do well. Through the star chart and reward system, we aim to make learning easy yet fun. With a smaller class size and step by step learning approach, we help the children to understand the creative and fun concepts. We also encourage the children to think on their feet and being able to solve the question independently. They will thus gain confidence and do even better and their potential will be unleashed.
Unleash Their Potential!
Chewy Math is founded in October 2014. We believe in the potential in every child to do well. Through the star chart and reward system, we aim to make learning easy yet fun. With a smaller class size and step by step learning approach, we help the children to understand the creative and fun concepts. We also encourage the children to think on their feet and being able to solve the question independently. They will thus gain confidence and do even better and their potential will be unleashed.

Adele Yeo  OrangeBelt
 Posts: 38
 Joined: Tue Jan 31, 2012 1:08 pm
 Total Likes: 0
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