Tutor MathsGuru: Ask me for your burning Maths questions!

[Dharma]

tutortamil:

Amelia has a stamp collection. 60% of them are Japanese stamps and the rest are Korean stamps. She gave away 63 Korean stamps and 25% of the Japanese stamps. She then had 5/8 of her stamp collection left. How many stamps did Amelia give away?


the ans is 105? i very close to figuring out but dont know one step.

Japanese : 60u - 15u = 45u
Korean : 40u - 63

3/8 => 15u + 63
1/8 => 5u + 21
8/8 => 40u + 168

100u = 40u + 168
60u = 168
15u = 42

Total stamps given away = 42 + 63 = 105

[Daddy]

Dear Maths guru,


Please help. Thanks.

1. Triangle ABC is a right-angle triangle. The area of the unshaded portion is 1/3 the area of the shaded portion. Find the area of triangle ABC.

http://www.postimage.org/image.php?v=aV9Uz90

Thanks

[starlight1968sg]

Area of unshaded triangle = 1/2 * 4 * 12 = 24cm2.


Thus area of shaded triangle = 24 * 3 = 72 cm2.

Area of triangle ABC = 24 + 72 = 96 cm2.

[Daddy]

Hi starlight1968sg,


"Area of unshaded triangle = 1/2 * 4 * 12 = 24cm2".
Why the area’s formula can applied on the triangle which is not a right angle?

24*3 ??? not understand.

thanks alot.

[ruyu]

Daddy:

Dear Maths guru,


Please help. Thanks.

1. Triangle ABC is a right-angle triangle. The area of the unshaded portion is 1/3 the area of the shaded portion. Find the area of triangle ABC.

http://www.postimage.org/image.php?v=aV9Uz90

Thanks

1/2 x 4 x 12 = 24

24 x 3 = 72

[ruyu]

Daddy:

Hi starlight1968sg,


\"Area of unshaded triangle = 1/2 * 4 * 12 = 24cm2\".
Why the area's formula can applied on the triangle which is not a right angle?

24*3 ??? not understand.

thanks alot.

it can be applied even if it is not an right angled triangle.

[starlight1968sg]

Daddy:

Hi starlight1968sg,


\"Area of unshaded triangle = 1/2 * 4 * 12 = 24cm2\".
Why the area's formula can applied on the triangle which is not a right angle?

24*3 ??? not understand.

thanks alot.

In any triangle, the formula half base * height holds. Note the height must be the vertical height ie it is perpendicular to the base. So in this case for the unshaded triangle, the base is 4 and the vertical height is 12. Thus the area is half of 48 = 24cm2.

Since area of unshaded is 1/3 of the area of shaded triangle ie 1 portion of unshaded and 3 portions of shaded.

Thus shaded triangle is 24 * 3 = 72cm2.

I hope my ans is correct!

[Daddy]

Thanks starlight1968sg for good explaination…

Thanks ruyu

[Dharma]

firebird:

Dear Dharma


Good morning.

Thank you very much for you help. I clearly understand now.

With best regards
Firebird

You're welcome, firebird.

[firebird]

Dear maths guru


Please help me on the following maths which were taken from Paper 2 CHIJ St Nicholas Girl’s School Preliminary Exam 2009:

Question 9,
I apologise for not inserting the diagram, which I am unable to.
The figure below is not drawn to scale. PQRS is a square and CBRD is a rectangle. BRE is a straight line. Given that angle DRF = 136 degree and angle SHD = 129 degree. Find the ratio of angle HRD to angle ERF.

Question 13,
Korey’s allowance to Skyler’s allowance was in the ratio 10:11. Both of them spent an equal amount. Then Korey’s remaining allowance was 7/9 of Skyler’s remaining allowance. What percentage of Skyler’s allowance did she spend? Leave your answer correct to 2 decimal places.

Question 17
At carpark P, the number of lorries to that of vans was in the ratio 3:7.
At carpark Q, the number of lorries to that of vans was in the ratio 8:9.
When 40% more lorries from an industrial estate entered carpark P and 20% of the vans at Q moved to carpark P, there were 76 fewer lorries at carpark P than Carpark Q. How many vehicles were there althogether at the two carparks finally?

Thank you
firebird