The problem can be represented on a Venn diagram, as shown below.
We have P(Day 1 ∩ Day 2) = 0.1 and P(Day 1) = 0.4
We can deduce that 30% of the group ONLY had sandwiches on Day 1 and there's 60% of the group ONLY had sandwiches on Day 2.
We obtain the value 60% = 0.6 from 100%-(10%+30%)=60%
We also can deduce that there 70% of the group that had sandwiches on Day 2
The proportion of people who ate sandwiches on Day 2 GIVEN that they ate sandwiches on Day 1 is given by
P(Day 1 ∩ Day 2)÷P(Day 2) = 0.1÷0.4 = 0.25 = 25%
The statement is TRUE
We have P(Day 1 ∩ Day 2) = 0.1 and P(Day 1) = 0.4
We can deduce that 30% of the group ONLY had sandwiches on Day 1 and there's 60% of the group ONLY had sandwiches on Day 2.
We obtain the value 60% = 0.6 from 100%-(10%+30%)=60%
We also can deduce that there 70% of the group that had sandwiches on Day 2
The proportion of people who ate sandwiches on Day 2 GIVEN that they ate sandwiches on Day 1 is given by
P(Day 1 ∩ Day 2)÷P(Day 2) = 0.1÷0.4 = 0.25 = 25%
The statement is TRUE