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.

## Wednesday, September 02, 2009

### Singapore Chinese Girls Sch 2008 PSLE Math Prelim Q48

At a farm, 40% of the animals are cows, 90% of the remainder are sheep and the rest are ducks. There are 56 more sheep than cows. After some cows died, 20% of the remaining animals at the farm are cows. How many cows are there left at the farm?

Solution

Cows ---- 40%
Remainder (sheep + ducks) ---- 100% - 40% = 60%

Sheep ---- 90% (remainder) x 60% = 54%

Sheep more than cows ---- 56
(Sheep) – (Cows) ---- 56
54% - 40% ---- 56
14% ---- 56
1% ---- 56 divided by 14 = 4

(Total) 100% ---- 100 x 4 = 400
(Sheep + ducks) ---- 60%
60% ---- 60 x 4 = 240

After some cows died 80% were sheep and ducks
80% ---- 240
1% ---- 240 divided by 80 = 3

(Cows left) 100% - 80% = 20%
20% ---- 20 x 3 = 60

Answer: There were 60 cows left.

#### 1 comment:

Anonymous said...

Cindy bought T-shirts at \$5 each and sold them at \$9 each. Those who bought two T-shirts from her were given one T-shirt free. At the end of the sale, Cindy earned a total of \$1288 and 120 T-shirts were given free. How many customers bought only one T-shirt?

Cost of the 120 T-shirts given away for free = 120 x \$5 = \$ 600
Profit for the rest of the T-shirts sold at \$9 each = \$1288 + \$ 600 = \$ 1888
Number of T-shirts sold = \$ 1888 / 4 = 472
Number of T-shirts sold with free T-shirts = 120 x 2 = 240
Number of customers who bought only one T-shirt each from Cindy = 472-240 = 232