Num certo bairro da cidade de Beira após o ciclone Idai, 120 voluntários trabalhavam de manhã, 130 trabalhavam à tarde, 80 trabalhavam à noite, 60 trabalhavam de manhã e a tarde, 50 trabalhavam de manhã e a noite, 40 trabalhavam à tarde e a noite e 20 trabalhavam nos três períodos. (a) Quantos voluntários trabalhavam em 2 períodos?

90 volunteers worked in 2 periods.

Step-by-step explanation: Venn Diagram is a diagram that shows all possible relations in a finite collection of diferent sets.

In this question, for example, the Diagram can be used to help solve it. The drawing of the diagram is in the attachment.

To complete the diagram, first you write the number that is common to the three circles, i.e., the number of volunteers who worked in the 3 periods: 20.

You know 60 worked on mornings and afternoon, so, since 20 already is in the diagram, in the space between morning and afternoon, the number is 40.

For mornings and nights: 50 - 20 = 30, so in the space between these thwo periods is 30.

For afternoons and nights: 40 - 20 = 20. In the space between the periods, the number is 20.

Adding the spaces between 2 periods, there is:

40 + 30 + 20 = 90

From all the volunteers, 90 worked in 2 periods.