This blog is managed by Song Hock Chye, author of Improve Your Thinking Skills in Maths (P1-P3 series), which is published and distributed by EPH.

Friday, July 11, 2008

S’pore Hokkien Huay Kuan 2007 PSLE Math Prelim Q48

Siti had some red and blue marbles. 80% of the marbles were red. After she bought another 63 red marbles and 46 blue marbles, 75% of the marbles were red. Find the total number of marbles she had at first.

Solution



(8 units – 6 units) + (63 – 138) ----- 75% - 75%
2 units – 75 ----- 0
2 units ----- 75
1 unit ----- 75/2

Total number of marbles at first
10 units ----- 75/2 x 10 = 375

Answer: She had 375 marbles at first.

Note – “The Singapore Hokkien Huay Kuan 5-School Combined Prelim Maths” is the common Maths Prelim Exam for Tao Nan, Ai Tong, Chongfu, Nan Chiau and Kong Hwa schools.

3 comments:

keentolearn said...

Dear Mr Song

Is it feasible to solve this problem with Model Drawing?
Please share how we could solve this problem by Model Drawing.

Best Wishes

Excel Eduservice said...

Yes, models can be used too. If you do that, you have to create a “before and after” scenario. You also have to make sure the “before” units must be distinct from the “after” units. That can be done by naming the “after” units as “parts” instead.

An example here.
http://road-to-psle.blogspot.com/2007/12/nan-hua-primary-school-psle-math-prelim_29.html

The above example is a “2-scenario” situation, which has the same characteristics as a “before and after” situation.

Back to Hokkien HK Q48 – The “before scenario” would have Red, Blue, 8 units, 2 units. “After scenario” would have Red, Blue, 3 parts, 1 part.

Red, 8 units + 63 ----- 3 parts
Blue, 2 units + 46 ----- 1 part

Carry on as in main post.

keentolearn said...

Dear Mr Song

Thank You for your quick reply.