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.

## Saturday, November 17, 2007

### Red Swastika School P5 CA2 2007 Math Question

Miss Chee bought some pencils, pens and notebooks. The number of notebooks she bought was 25% of the number of pens. The cost of a pencil, a pen and a notebook was \$2, \$3 and \$7 respectively. The total cost of the pens and notebooks were \$418 and the total cost of the pencils and notebooks were \$262. How many pencils did Miss Chee buy?

Pencils (unknown no. of pencils) ----- ? x \$2 each
Pens ----- 4 units x \$3 each ---- 12 units (of dollars)
NB ----- 1 unit x \$7 each ----- 7 units (of dollars)
("Pens" has been allocated 4 units while "NB" 1 unit because the number of NBs bought is 25% of the number of pens)

Pens + NB ----- \$418
12 units + 7 units ---- \$418
19 units ----- \$418
1 unit ------ \$418/19 = \$22 (the all important 1 unit)

Pencils + NB ----- \$262
? x \$2 + 7 units ------ \$262
? x \$2 + (7 x \$22) ----- \$262
? x \$2 + \$154 ----- \$262
? x \$2 ----- \$262 - \$154 = \$108
? ---- \$108/\$2 = 54