Q&A - PSLE Math

[tianzhu]

Hi P5G


Rick ate twice as much as his brother.
Divide a pizza into 3 parts.
2 parts ----- Rick
1 part ------ His brother
His brother ate 1/3 of a pizza


7/8 of a log cake is distributed to 1 twin sister and 2 brothers. The three of them shared equal portions.
7/8 ÷ 3 or 7/24.

Best wishes

[P5G]

tianzhu:

Hi P5G


Rick ate twice as much as his brother.
Divide a pizza into 3 parts.
2 parts ----- Rick
1 part ------ His brother
His brother ate 1/3 of a pizza


7/8 of a log cake is distributed to 1 twin sister and 2 brothers. The three of them shared equal portions.
7/8 ÷ 3 or 7/24.

Best wishes

Uncle Tianzhu,

Why do you multiply by 7/8 for the log cake but not by 2 for the pizzas?
How do we decide when to multiply by the number given and when not to?
Your help will be greatly appreciated.

TIA.

[tianzhu]

Hi P5G


The question asks a student to find out what fraction did Rick’s brother eat.

Rick ate twice as much as his brother.
Therefore, Rick ----- 2 units and his brother ----- 1 unit.

You may just work on one pizza
Divide a pizza into 3 parts.
Rick ----- 2 parts
His brother ------1 part

His brother ------ 1/3 of a pizza

If you choose to work with 2 pizzas.
One pizza ----- 3 parts, therefore 2 pizzas -------6 parts
Rick ----- 4parts
His brother ------2 parts

The answer is 2/6 which is also 1/3

Best wishes

[tianzhu]

Hi


Imagine a piece of log cake cut into 8 big pieces.

Out of these 8 pieces, 7 pieces are distributed to 1 twin sister and 2 brothers.

Further subdivide these 7 pieces into 21 smaller pieces to be shared among the 3 people.

Hence each one of them (1 twin sister and 2 brothers ) receives 7 smaller pieces each.

There are a total of 24 smaller pieces in the beginning.(The whole log cake)

Hence, 7/24

Best wishes

[P5G]

tianzhu:

Hi


Imagine a piece of log cake cut into 8 big pieces.

Out of these 8 pieces, 7 pieces are distributed to 1 twin sister and 2 brothers.

Further subdivide these 7 pieces into 21 smaller pieces to be shared among the 3 people.

Hence each one of them (1 twin sister and 2 brothers ) receives 7 smaller pieces each.

There are a total of 24 smaller pieces in the beginning.(The whole log cake)

Hence, 7/24

Best wishes

Uncle Tianzhu,

Thank you for your clear explanations. So for the log cake, we are talking about a 'whole' log cake and not just 7/8.

Will the answer be just 1/3 if \"of a\" is removed from the question as follows:
Nomee distributed 7/8 log cake equally among her twin sister and 2 brothers. What fraction of the log cake did each of them receive?

TIA.

[ozora]

MathIzzzFun:

ozora:

Got this question:

The ratio of the number of pupils in class A to the number of pupils in class B is 5: 4 at first. 1/5 of the pupils in class A and 7/8 of those in class B were girls. After reshuffling of pupils between 2 classes, the number of boys in each class is equal to the number of girls. If the total of 24 pupils are affected, how many pupils are there in each class at first?
I got the answer class A-42 and B-30 which are wrong.
Anyone can help?
Answer is class A-40 and B-32

Hi

a model approach

http://www.flickr.com/photos/62167097@N02/5834499397/in/photostream

thanks MathIzzzFun
cheers.

[ozora]

MathIzzzFun:

ozora:

Got this question:

The ratio of the number of pupils in class A to the number of pupils in class B is 5: 4 at first. 1/5 of the pupils in class A and 7/8 of those in class B were girls. After reshuffling of pupils between 2 classes, the number of boys in each class is equal to the number of girls. If the total of 24 pupils are affected, how many pupils are there in each class at first?
I got the answer class A-42 and B-30 which are wrong.
Anyone can help?
Answer is class A-40 and B-32

Hi

a model approach

http://www.flickr.com/photos/62167097@N02/5834499397/in/photostream

cheers.

thanks but why is it cut into 4 units for the class A and 2 units each for class B?

[MathIzzzFun]

ozora:

MathIzzzFun:

[quote=\"ozora\"]Got this question:

The ratio of the number of pupils in class A to the number of pupils in class B is 5: 4 at first. 1/5 of the pupils in class A and 7/8 of those in class B were girls. After reshuffling of pupils between 2 classes, the number of boys in each class is equal to the number of girls. If the total of 24 pupils are affected, how many pupils are there in each class at first?
I got the answer class A-42 and B-30 which are wrong.
Anyone can help?
Answer is class A-40 and B-32

Hi

a model approach

http://www.flickr.com/photos/62167097@N02/5834499397/in/photostream

cheers.

thanks but why is it cut into 4 units for the class A and 2 units each for class B?[/quote]hi

number of students in Class A n Class B in ratio of 5 : 4 = 20 units : 16 units

given also : 1/5 of Class A and 7/8 of Class B are girls. So,

1/5 of 20 units = 4 units
1/8 of 16 units = 2 units

cheers.

[tianzhu]

P5G:

Uncle Tianzhu,

Thank you for your clear explanations. So for the log cake, we are talking about a 'whole' log cake and not just 7/8.

Will the answer be just 1/3 if \"of a\" is removed from the question as follows:
Nomee distributed 7/8 log cake equally among her twin sister and 2 brothers. What fraction of the log cake did each of them receive?

Hi P5G

Good Morning.

Nomee distributed 7/8 of a log cake equally among her twin sister and 2 brothers. What fraction of the log cake did each of them receive?

In this question, having some form of pictorial representation does help one to see the relationship.

This question touches on “Product of Proper Fractions” which is covered in P5.

Students who are familiar with it can write a number sentence 7/8÷3 or 7/8*1/3 and arrive at an answer of 7/24.

If you rewrite the question as

Nomee ate 1/8 of a log cake and distributed the remainder equally among her twin sister and 2 brothers. What fraction of the remaining part of the log cake did each of them receive?

The answer is 1/3.

Usually, you'll be asked to find the fraction of a whole.

Best wishes

[KSP]

Hi need help here. Thanks.


Lily is meeting a friend at a certain time. If she drives at 80km/h, she will be 1/3 hr late. If she drives at 60km/h, she will be 3/4hr late. How long will the journey take if she drives at 90km/h?