Q&A - PSLE Math

[tianzhu]

Michaelia0816:

A square is incribed in a circle. If the area of the square is 70cm2, what the area of the circles? (Take pi as 22/7)

Hi

Please take a look at this similar question.

Area of the outer square ------ 140

140 ------ d*d where d is the diameter of the circle.

Area of circle -----pi*d^2/4 ----- 22/7*140/4 ------ 110

Hope this helps.

Best wishes

http://farm7.staticflickr.com/6151/6191262010_71cc0ec1fd_z.jpg\">

[Michaelia0816]

Do the 140cm2 get by 70cm2*2

[Michaelia0816]

Now I understand how 140cm2 is get

[Michaelia0816]

Thx :finally finished!:

[charsen]

tianzhu:

charsen:

How to solve this question ?

The sum of 4 numbers is 80.If you add 3 to the first number, subtract 3 from the second number,multiply the third number by 3 d divide the fourth number by 3,the result will be equal.What is the difference between the largest and the smallest of the original numbers.

Hi

First thing first, is such a question within the syllabus?

The original numbers are 12,18,5 and 45.

Difference ------ 45-5 ------ 40

Best wishes

How do you get this numbers?Is It By logical reasoning?I think this is in the syllabus.

[lucky168]

Has anyone used the assessment book "Top school maths, Volume 4A" by Edmund Cheong, Derek Cheong & Vincent Seow? It’s horrible! Has found 4 mistakes so far after doing just 2 papers!

[MathIzzzFun]

charsen:

How to solve this question ?

The sum of 4 numbers is 80.If you add 3 to the first number, subtract 3 from the second number,multiply the third number by 3 d divide the fourth number by 3,the result will be equal.What is the difference between the largest and the smallest of the original numbers.

hi

Hi
after multiplying 3rd number by 3 --> 3u

1st number --> 3u-3
2nd number --> 3u +3
3rd number --> 1u
4th number --> 9u
Total --> 16u = 80
1u --> 5

1st number --> 12
2nd number --> 18
3rd number --> 5
4th number --> 45

cheers.

[MathIzzzFun]

dicoyote:

Hi MathIzzzFun,

Thank you so much, am amazed at the details you have provided, not only that, even applying side by side with the \"chicken & cow\" logic, which make understanding more easier

Just to clarify my understanding, the \"x3\" uses across for the value is to find a similarity basis for the equation, am I correct? :scratchhead:

Hi

In a \"normal\" chicken-cow type of question, we will have
1 cow --> 4 legs
1 chicken --> 2 legs, OR
1 pen --> $4
1 pencil --> $2

For this question, we have:
Amount collected for 2 vases delivered on time --> $15
Amount collected for 3 vases delivered late --> $10

A straightforward way is to find the unit value :
Amount collected for 1 vase delivered on time --> $ 7.50
Amount collected for 1 vase delivered late --> $10/3 -- not a whole number, and not a \"nice\" fraction like 1/2.
difference --> $7.50 - $10/3 = $ 25/6 -- amount collected less due to late delivery.

We can proceed normally as follows:
If all vases delivered on time, amount collected --> 500 x $7.50 = $3750
$3750-$3675 = $75
$75 ÷ $25/6 = 18 --> 18 vases were delivered late.

To avoid with fractions, we can \"normalize\" the numbers -- $15 & $10, make multiple of 15 & 10 --> 30, 60, 90...- 60 is the ideal choice

So, Amount collected for 3 vases delivered late --> $10 -- 30 units ie $1 --> 3 units
Amount collected for 2 vases delivered on time --> $15 --- 45 units


So, amount collected for 1 vase delivered on time --> 22.5 units
amount collected for 1 vase delivered late --> 10 units


cheers.

[Winx5015]

Hi, got problem with math questions again . Sigh...


(1) Adrian, Ben and Calvin share 436 marbles. After Adrian gave away 2/5 of his marbles, the ratio of the number of marbles he has to Ben became 4:9. When Calvin lost 1/3 of his marbles, the total number of marbles the children has was 352. How many marbles did Calvin have at first?

(2) Jodie has 20% more red beads than green beads. She has 50 more orange beads than red beads. She mixed 20% of each of the coloured beads to make a total of 22 bracelets. She had used 298 red and orange beads for all the bracelets. How many beads were there in each bracelet?

Thanks

[MathIzzzFun]

Winx5015:

Hi, got problem with math questions again . Sigh...


(1) Adrian, Ben and Calvin share 436 marbles. After Adrian gave away 2/5 of his marbles, the ratio of the number of marbles he has to Ben became 4:9. When Calvin lost 1/3 of his marbles, the total number of marbles the children has was 352. How many marbles did Calvin have at first?

Thanks

Hi

After Adrian gave away 2/5 of his marbles :
Adrian's marbles : Ben's marbles --> 4 : 9 --> 12u : 27u --total 39u
Number given away by Adrian --> 8u

Calvin's marble --> 3p, lost --> 1p
Marbles given away & lost, 8u + 1p = 436-352 = 84 -- (1)
Marbles left, 39u + 2p = 352 ---(2)
Solving (1) & (2), 1u --> 8, 1p --> 20

Number of marbles Calvin had at first --> 3 x 20 = 60

cheers.