295 pupils from Bukit View, Sungei Road and Changi Primary Schools took part in a National Day parade. The number of boys from each school who took part was the same. 20% of the pupils from Bukit View, 40% of the pupils from Sungei Road and 50% of the pupils from Changi were girls. Find the total number of girls who took part in the parade.
Need a hint?
Work out what fraction of each school is boys first. Since the boys are equal, the school sizes are in inverse proportion to those fractions.
Worked answer
- Boys are 45 of Bukit View, 35 of Sungei Road and 12 of Changi.
- Make the numerators equal: 45 = 1215, 35 = 1220, 12 = 1224.
- The boys are equal (12 units each), so the schools have 15, 20 and 24 units.
- Total = 15 + 20 + 24 = 59 units = 295 pupils, so 1 unit = 5.
- Bukit View 75, Sungei Road 100, Changi 120 pupils.
- Girls: 20% of 75 = 15, 40% of 100 = 40, 50% of 120 = 60.
- Total girls = 15 + 40 + 60 = 115.
Answer: 115 girls
The mistake this question tests
Habit
Stopped at one part in ratio
Pupils often assume the three schools sent the same number of pupils. The equal number of boys must be used to find each school's size first.
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