Q&A - PSLE Math

[iFruit]

mum2010:

Please help!


Benny has 24 notes which totals to $168. They are in two-dollar, five-doller adn ten-dollar denominations. How many of each kind of notes does he have?

10x + 5y +2z = 168

Now, z can only be 4 or 9 or 14 and so on, as 10x +5x can only be a multiple of 10.

z can't be 9 ( or higher), because then the remaining notes will be 15 and all of them will have to be $10 notes. So z = 4.

Then

10x + 5y = 160
x +y = 20 ---> 5x + 5y = 100

From the 2 equations we get, x = 12, y= 8

so $10 = 12; $5 = 8, $2 = 4;

HTH

[Florence88]

If anybody can help to solve some of the problem sums listed below.


1) A's pocket money is 20% more than B, but 20% less than C. If their total pocket money is $2,220, find the amount each individual has ?

2) Tap A takes 5 mins to fill 1/4 of a container while tap B takes 10 min. If both the taps are turned on at the same time, how long does it take to fill up the container ?

3) The ratio of boys to girls was 3:2. After 2 boys and 3 girls joined in, the ratio became 4:3. How many girls were there at first ?


Thanks for the help :?

[Andrew Lee]

Hi...

http://postimage.org/image/n5mxfo1w/
:?

[iFruit]

Florence88:

If anybody can help to solve some of the problem sums listed below.


1) A's pocket money is 20% more than B, but 20% less than C. If their total pocket money is $2,220, find the amount each individual has ?

Assume B's pocket money = 100u

A's pocket money = 120u

C's pocket money = 100/80 x 120u = 150u

A+B+C = 100u + 120u +150u = 370u = 2220-----> u =6

A = 120u = 720
B = 100u = 600
C = 150u = 900

[iFruit]

Florence88:

If anybody can help to solve some of the problem sums listed below.


2) Tap A takes 5 mins to fill 1/4 of a container while tap B takes 10 min. If both the taps are turned on at the same time, how long does it take to fill up the container ?

Tap A takes 5 mins to fill 1/4 of a container --->Tap A takes 1 mins to fill 1/20 of a container

Tap B takes 10 mins to fill 1/4 of a container --->Tap B takes 1 mins to fill 1/40 of a container

In 1 min, Tap A & B fill = 1/20 + 1/40 = 3/40 of the container

Time taken to fill the container = 40/3 = 13 1/3 mins

[iFruit]

Florence88:

3) The ratio of boys to girls was 3:2. After 2 boys and 3 girls joined in, the ratio became 4:3. How many girls were there at first ?


Thanks for the help :?

Let girls = 2u
Boys = 3u

3u +2: 2u+3 = 4:3

3(3u+2) = 4(2u+3)---> 9u +6 = 8u +12---->u=6

girls at first = 2u = 12

HTH.

[Yu Xuan]

tianzhu:

mum2010:

Mary put some fifty-dollar notes and some ten-dollar notes into a piggy bank. There were a total of 60 notes. The total value of the fifyt-dollar notes and ten-dollar notes was equal. How much money did she put into the piggy bank?

Hi

Consider an equal value of $10.
You’ll have 1 number of $10 note and 2 number of $5 note. Altogether, you’ll have $20 and a total number of 3 notes.

Given that there are 60 notes altogether.

3 notes ------ $20
60 notes ------- S400

Best wishes

Hi Tianzhu

Should be $50 and $10.

Hence to equate the value
$50 --> 1 unit
$10 --> 5 units

6units --> 60
1 unit --> 60 / 6 = 10
5 units --> 10 * 5 = 50

($50 x 10) + ($10 x 50) =$1000

Is this answer correct?

[iFruit]

Andrew Lee:

Hi...

http://postimage.org/image/n5mxfo1w/
:?

Since we only need the sum

sum of angles a, b, c, d ,e = three triangles - (angles not including a,b,c,d,e) = 180 + 180 +180 - (180-20) - (180-120) = 540 - 160 -60 = 320

[tianzhu]

Hi Yu Xuan


Good Morning.

You’re correct. I’ve made a mistake in my earlier post by using $5 instead of $50.

Thank you for your correction.

Consider an equal value of $50.
You’ll have 1 number of $50 note and 5 number of $10 note. Altogether, you’ll have $100 and a total number of 6 notes.

Given that there are 60 notes altogether.

6 notes ------ $100
60 notes ------- $1000

Best wishes

[Yu Xuan]

Hi Tianzhu


Would you interpret the following statements as similar;

20% X $100 =$20

20/100 X $100 =$20

Especially the first statement, do you think it is acceptable?

Thank you.

Yu Xuan