Question

There are 135 people in a sport centre. 73 people use the gym. 59 people use the swimming pool. 31 people use the track. 19 people use the gym and the pool. 9 people use the pool and the track. 16 people use the gym and the track. 4 people use all three facilities. How many people didn't use any facilities?​

Answer 1

24 people

Explanation:

((The numbers are up there, so I am not going to define each variable.))

For starters, there is no overlap between the double facilities groups, except the triple facility users, so:

19 + 9 + 16 - 4 = 40 people

Since there is overlap between single and double groups, you will need to subtract, so:

Gym: 73 - 19 - 16 = 38

Pool: 59 - 19 - 9 = 31

Track: 31 - 9 - 16 = 6

Total for 1 facility: 38 + 31 + 6 - 4 = 71 people

((Minus 4 because the 4 triple facility users overlap the double facility users (problem is in layers: layer 1 minus layer 2, then minus layer 3).))

Next, add the totals:

71 + 40 = 111 people (using facilities)

135 - 111 = 24 people (who didn't use any)

(((I'm not 100% sure on this answer, so if someone could check my work, that would be much appreciated.)))