Q&A - PSLE Math

[tianzhu]

Hi insider


Thank you for pointing out the errors.

I’ll amend the original posts.

Best wishes

[small]

Please help on the following question (from my DS's Maths homework book) and many thnaks in advance.


Question
In a pastry shop, the number of cakes was twice the number of cream puffs. After 90 cakes and 42 cream puffs were sold, the ratio of the number of cakes left to the number of cream puffs left was 2 : 5. How many cakes and cream puffs were in the shop at first?

[YumYum]

Hi, can anyone pls help on the Qn below:


A farm has some ducks and cows. The ratio of the number of animals to the total number of legs is 8:23. Express the number of ducks as a fraction of the cows. Give yr answer in the simplest form.

many thanks

[small]

YumYum:

Hi, can anyone pls help on the Qn below:


A farm has some ducks and cows. The ratio of the number of animals to the total number of legs is 8:23. Express the number of ducks as a fraction of the cows. Give yr answer in the simplest form.

many thanks

HTH, I learnt the solution from MathIzzzFun and tianzhu.


Total number of legs had to be even, so 8 : 23 >> 16 : 46

Now if all 16 are ducks, then there will be 16 X 2 = 32 legs, thus there are 14 extra legs (46 - 32)

Note that if we were to replace each duck with a cow, then we can increase the number of legs by 2.

Since there are 14 extra legs, 14 /2 = 7 thus there are 7 cows.

So there are 9 ducks and 7 cows.

Fraction of ducks / cows = 9/7.

[tianzhu]

small:

Please help on the following question (from my DS's Maths homework book) and many thnaks in advance.


Question
In a pastry shop, the number of cakes was twice the number of cream puffs. After 90 cakes and 42 cream puffs were sold, the ratio of the number of cakes left to the number of cream puffs left was 2 : 5. How many cakes and cream puffs were in the shop at first?

Hi small

Please check your question with your source.

Best wishes

[small]

Another solution which using algebra method.


Let:
D – Ducks (2legs)
C – Cows (4legs)

Total number of these animals -> D+C
Total number of their legs -> 2D+4C

(D+C)/(2D+4C)= 8/23
23D+23C=16D+32C
7D=9C
D/C = 9/7

Fraction of ducks / cows = 9/7.

[small]

tianzhu:

small:

Please help on the following question (from my DS's Maths homework book) and many thnaks in advance.


Question
In a pastry shop, the number of cakes was twice the number of cream puffs. After 90 cakes and 42 cream puffs were sold, the ratio of the number of cakes left to the number of cream puffs left was 2 : 5. How many cakes and cream puffs were in the shop at first?

Hi small

Please check your question with your source.

Best wishes

Thanks tianzhu, will ask my DS check with his form teacher.

This question is Q7 page 70 of 'My PALS Are Here Maths Homework (2nd Editon) 6A'

[tianzhu]

Hi small


Good Morning.

You’ll get an answer in decimals.

Cake: cream puffs ------ 2 units: 1 unit
Cake: cream puffs ----- -90: -42
Cake: cream puffs ------ 2 parts: 5 parts

Cross multiply or equalising the parts

10 units – 450 ------ 2 units – 84
8 units ------- 366
1 unit ------- 45.75

Hence, you’ll end up with 3*45.75 or 137.25 cakes and cream puffs at first.(not in whole number)

Best wishes

[small]

Good morning tianzhu,


We also got 8U = 366, my DS said may be somebody ate the cake and puff..

[MathIzzzFun]

small:

Good morning tianzhu,


We also got 8U = 366, my DS said may be somebody ate the cake and puff..

good morning!

haha.. I think the question was likely adapted by changing only names of items - if the cakes and puffs are replaced by kg of flour and kg of sugar, then the answer will make sense