Question

how many customers younger than 40 years old came into the store?
2
6
11
4

Explanation:

Step1: Identify age - groups younger than 40

The age - groups are 20 - 30 and 30 - 40.

Step2: Find the frequencies of relevant age - groups

The frequency of the 20 - 30 age - group is 2 and the frequency of the 30 - 40 age - group is 4.

Step3: Calculate the total number of customers

Add the frequencies: $2 + 4=6$.

Answer:

6