If 10% of a group ate sandwiches two days in a row, and 40% of the group had a sandwich on the first day, this means that 25% of the group that ate a first sandwich had a second.
lets say there were 100 people and 40 ate sandwiches on the first day then 25 percent of 40 is 10, so 10 had sandwiches two days in a row i would say it is true