PSLE
School camp sweaters were available in 4 colours: black, pink, green and blue. At the camp, each contestants chose one sweater. The pie chart represents the contestants' choice of sweater colours. 39 contestants chose blue sweaters. The contestants' choice of sweater colours is also represented by the bar graph. The bar that shows the number of contestants who chose black sweaters has not been drawn. How many contestants chose black sweaters?

    
From the pie graph,
fraction of contestants who chose green or pink
= ^90°_360°
= ¹₄

From the bar graph,
Number of contestants who chose green = Number of contestants who chose pink = 54 

¹₄ of the pie chart = 54
⁴₄ of the pie chart = 4 x 54 = 216

Total number of contestants = 216

Number of contestants who chose black sweaters
= 216 - 54 - 54 - 39
= 69

Answer(s): 69