Question

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what percentage of students were younger than 30 years old?
how many students were at least 43 years old?
how many students were 19 years old?

Explanation:

Step1: Count total number of students

Count all the dots in the dot - plot. Let's assume there are $n$ dots. After counting, $n = 50$.

Step2: Find number of students younger than 30

Count the dots for ages 15 - 29. There are 30 dots for ages 15 - 29. The percentage of students younger than 30 is $\frac{30}{50}\times100\%=60\%$.

Step3: Find number of students at least 43

Count the dots for ages 43 - 50. There are 7 dots for ages 43 - 50.

Step4: Find number of students 19 years old

Count the dots for age 19. There are 12 dots for age 19.

Answer:

What percentage of students were younger than 30 years old? 60%
How many students were at least 43 years old? 7
How many students were 19 years old? 12