Q&A - PSLE Math

[MathIzzzFun]

Petkwang:

Hi All,


Can someone help to solve these questions by using model. Thank you.

A total of 510 people visited a book exhibition,. 5/8 of the male visitor and 1/3 of the female visitors were adults. There were twice as many girls as boys. How many more men than women visited the book exhibition?


There are 98 pieces of $20 notes and $50 notes in a drawer, A cashier took out 3/4 of the $50 notes and put in another ten $20 notes. As a result, the number of $20 notes was five times the number of $50 notes. What was the total value of the $20 notes in the drawer at first?

Hi

Q1.
Number of boys : men --> 3u : 5u
Number of girls : women --> 6u : 3u
Total number of visitors --> 17u -- 510
1u --> 30
2u --> 60, there were 60 more men than women

Q2.
In the end, number of $20 notes : $50 notes --> 5u : 1u
At first, number of $50 notes --> 4u
5u + 4u = 9u --> 98 + 10 = 108
9u --> 108
1u --> 12
Number of $20 notes at first --> 5u - 10 = 50, value of $20 notes --> 50 x $20 = $1000

cheers.

[homeworkmummy]

Is there something wrong with the following question? The question is extracted from Ai Tong paper CA1 2011. The total is actually more than 100%…


In a survey, some pupils were asked if they preferred volleyball or table tennis. 13/20 of the pupils chose volleyball, 75% of the pupils chose table tenis and 5% of the pupils did not chose any of the two sports. Given that 90 pupils chose both volleyball and table tennis, how many pupils took part in the survey?

[elkniwt]

homeworkmummy:

Is there something wrong with the following question? The question is extracted from Ai Tong paper CA1 2011. The total is actually more than 100%....


In a survey, some pupils were asked if they preferred volleyball or table tennis. 13/20 of the pupils chose volleyball, 75% of the pupils chose table tenis and 5% of the pupils did not chose any of the two sports. Given that 90 pupils chose both volleyball and table tennis, how many pupils took part in the survey?

Hi homeworkmummy,

This question is a venn diagram type of question. To find the overlap between volleyball and table tennis, take 3/4 + 13/20 - (1 - 1/20) = 9/20
9/20 -> 90 pupils
1/20 -> 10 pupils
20/20 -> 200 pupils
Hence, 200 pupils took part in the survey.

Regards.

[MathIzzzFun]

homeworkmummy:

Is there something wrong with the following question? The question is extracted from Ai Tong paper CA1 2011. The total is actually more than 100%....


In a survey, some pupils were asked if they preferred volleyball or table tennis. 13/20 of the pupils chose volleyball, 75% of the pupils chose table tenis and 5% of the pupils did not chose any of the two sports. Given that 90 pupils chose both volleyball and table tennis, how many pupils took part in the survey?

Hi

use Venn Diagram to solve.

5% did not choose any of the sports --> 95% chose either table-tennis or volleyball or both

75% chose table tennis --> (95% - 75%) = 20% chose volleyball only.
65% chose volley ball --> (65%-20%) = 45% chose both volleyball and table tennis
45% --> 90, 1% --> 2, 100% --> 200
200 pupils participated in the survey.

cheers.

[homeworkmummy]

Hi Elkniwt and MathIzzzFun, thank you so much for your help!

[Petkwang]

Thanks

[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.