Answer:
4 tours.
Explanation:
Let x represent number of tours.
We have been given that 4 tour groups took a trip to the national museum. There are 35 people in each group.
Let us find total number of people in 4 groups.


We are also told that a maximum of 40 people were allowed on a tour at 1 time. So people who will see museum in x tours would be
.
The number of people who will visit museum in x tours should be greater than or equal to 140.



Since we cannot take 0.5 of a tour, therefore, the least number of tours that needed for all the people to take the tour would be 4.