1. Histograms Objectives: A Grade Interpret a histogram with unequal class intervals Prior knowledge: Draw a Histogram diagram

2. Histograms Finding Frequencies 0 10 20 30 40 50 60 2 1 Frequency density Length (cm) How many lengths are in the class interval 40cm to 60cm? 20 1 20 x 1 = 20 How many lengths are in the class interval 30cm to 40cm? 10 x 2 = 20 2 10 What is the total frequency?Repeat for the other bars. 10 x 1.5 = 15 20 x 1 = 20 20 + 20 + 20 +15 = 75 75

3. Histograms From this histogram you could be asked further questions: 0 10 20 30 40 50 60 70 3 2 1 Frequency density Age (years) Estimate how many people between the ages of 35 and 55 surf. Identify the area of the bars to which this applies. 35 55 Remember: frequency is the area Find the area separately of each bar 5 1.2 15 1313 5 × 1.2 = 6 15 × 1 = = 5 3 Estimate of the frequency = 6 + 5 = 11

4. Histograms Estimate the median from this histogram 110 120 130 140 150 160 170 4 3 2 1 Frequency density height (cm) Histogram of children’s heights Find the total frequency, then find which class interval it is in, draw a line in the bar where the median is represented to find where it is on the x axis 15 × 1 = 15 5 × 3.6 = 18 5 × 3.4 = 17 5 × 4 = 20 10 × 2.5 = 25 10 × 2 = 20 10 × 0.5 = 5 Frequency 15+18+17+20+25+20+5 = 120 median position = 60 Where is this? 1533 50 60 The median is approximately 137.5 cm