Q&A - PSLE Math

[turquoise]

Thanks Dharma.

[Dharma]

turquoise:

Thanks Dharma.

No pbm

[faith2u]

Hi everyone, I need help in the below questions…thanks in advance.


1). In a Primary school of 1960 students, ¼ of the boys and 1/5 of the
girls make up 400 children. How many girls are there? (Ans : 1800)

2). A carp cost $12. A goldfish cost 75% less than a carp. Ramli bought
some carps and goldfish for $198. 60% of the fish he bought were
goldfish.
(a). how many carps did he buy? (Ans : 12)
(b). how many goldfish did he buy? (Ans : 18)
. how much more money did he spend on the carps than goldfish?
(Ans : $90)

3). Mr Huang knocked 160 nails along the perimeter of the ceiling of a
function room measuring 20m long by 12m wide. The distance
between each nail was equal. He hung 3 balloons on each nail.
(a). how many nails were knocked along the width of the ceiling?
(ans : 31 nails)
(b). how many balloons did he buy in all if he has 20 left? (ans : 500)

[faith2u]

Hi everyone, here is another set of question which I need help…thks.


1). Uncle Seng bought some fruits. 1/3 of the fruits were apples, 1/9 of
them were mangoes and the rest were oranges. The prices of the
fruits are as shown :
Apples – 20cents each
Mangoes – 70cents each
Oranges – 30cents each
Uncle Seng spent $15.60 on the apples and mangoes. How much did
he spend on the oranges? (ans : $18 )

2). Meili has a total of 20 mangoes and oranges. If she exchanges every
mango for 3 oranges, she will have 32 oranges. How many oranges
does she have? (ans : 6).

3). Tank A and tank B had 48litres and 8litres of water respectively at
first. Then an equal amount of water was added into each tank. As a
result, the ratio of the amount of water in tank A to that of tank B
became 3:1. How much water was added into each tank?

4). Meimei would be given 20cents for each greeting card she sold. In
addition, she would get $4 for every 10 greeting cards scold. How
many cards did she sell if she earned $80?

[kitty2]

Please help to solve these 2 problems,thanks


1)Find the sum of all the odd numbers from 1 to 210


2)The ratio of the number of horses to the number of cows is 3:8.The number of sheep is twice the number of horses.After 30 cows were sold,1/4 of the remaining animals were cows.What was the total number of sheep and horses?

[bwpj2000]

1)Sum of first 2 odd numbers = 1+3 = 4

Sum of first 3 odd numbers = 1+3+5 = 9
Therefore sum of the first n odd numbers is n^2
So sum of first 210 odd numbers is 210^2= 44100

Not too sure about Q2. :?

[Dharma]

bwpj2000:

1)Sum of first 2 odd numbers = 1+3 = 4

Sum of first 3 odd numbers = 1+3+5 = 9
Therefore sum of the first n odd numbers is n^2
So sum of first 210 odd numbers is 210^2= 44100

Not too sure about Q2. :?

Q1 Sum of odd nos. from 1 to 210 = (210/2) x (210/2) = 11025

To derive :
Sum of all nos. from 1 to 210 = 105 x 211 = 22155 (210 x 211)/2
Sum of all even nos. from 1 to 210 = 2(1+2+...+104+105) =2(105 x 106)/2 = 11130
So, (1+3 + ...+ 209) = 22155 - 11130 = 11025

[bwpj2000]

Oops. :oops:

Sorry, my bad.

[kitty2]

[

To derive :
Sum of all nos. from 1 to 210 = 105 x 211 = 22155 (210 x 211)/2
Sum of all even nos. from 1 to 210 = 2(1+2+...+104+105) =2(105 x 106)/2 = 11130
So, (1+3 + ...+ 209) = 22155 - 11130 = 11025[/quote]

Thanks for the answer,where do you get the 105 from? :?:

[john.09525316]

bwpj2000:

1)Sum of first 2 odd numbers = 1+3 = 4

Sum of first 3 odd numbers = 1+3+5 = 9
Therefore sum of the first n odd numbers is n^2
So sum of first 210 odd numbers is 210^2= 44100

Not too sure about Q2. :?

In fact your approach is good, except the last part should be
n= 210/2 = 105

Therefore, the answer is 105*105 = 11025