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.

## Tuesday, April 14, 2009

### Rosyth Sch 2006 PSLE Math Prelim Q43

Mrs Yu paid \$16.20 for some eraser and pencils. An eraser cost 15 cents and a pencil cost 45 cents. She bought 12 more pencils than erasers. How many erasers did she buy?

Solution

1 eraser ----- \$0.15
1 pencil ----- \$0.45
1 set (of 1 eraser, 1 pencil) ----- \$0.60

She bought -----
Unknown number of sets + 12 pencils ----- \$16.20
(? x \$0.60) + (12 x \$0.45) ----- \$16.20
(? x \$0.60) + \$5.40 ----- \$16.20
? x \$0.60 ----- \$16.20 - \$5.40 = \$10.80
? ----- \$10.80 divided by \$0.60 = 18 (sets)

18 sets ----- 18 erasers

Anonymous said...

lousy method! USE HEURISTICS

xiaorou said...

Hi anon@0313

Please do not hide under the veil of anonymity and pass discouraging remarks.

Mr Song's blog is very useful for those PSLE kids who do not have the previleges of tuition.Not every student can afford to get external help.

Mr Song helps to provide meaningful materials free for which we should be grateful.

If you have better solutions, please share.

Anonymous said...

hey, Mr Song is your uncle, is it? Why so protective? The methods is so confusing and will make students even more confuse! Share? Why?

Anonymous said...

hey, Mr Song is your uncle, is it? Why so protective? The methods is so confusing and will make students even more confuse! Share? Why?

Tilted Earth said...

Hi

To many less privileged kids, Mr Song is like a kind uncle who shares his resources unselfishly. He didn’t claim they are the best solutions, but for those kids without external help, they are good enough. For those who are more blessed with alternative resources, please be more tolerant and understanding towards others.

Tilted Earth said...

Hi

To many less privileged kids, Mr Song is like a kind uncle who shares his resources unselfishly. He didn’t claim they are the best solutions, but for those kids without external help, they are good enough. For those who are more blessed with alternative resources, please be more tolerant and understanding towards others.

Anonymous said...

any relative again!

Anonymous said...

Number Cost Total Cost

Eraser 1u 15 15u
Pencils 1u+12 45 45u+540

Total 60u+540

60u+540=1620
60u= 1080
1u = 18

Anonymous said...

the anonymous person who said this method is lousy, then wat other method is there? Care to share?

Anonymous said...

can anyone tell me why can't the following method work?

12x\$0.45=\$5.40
\$16.20-\$5.40=\$10.80
\$10.80/2=\$5.40
\$5.40/\$0.15=36 erasers

pls tell me pls thx a lot! :D