How to solve 3x-2y=4
1 answer:
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Not sure why, but I wasn't able to post my solution as text, so I've written it elsewhere and am posting screenshots of it here.
In the fifth attachment, the first solution is shown above the second one.
We need to determinate who doesn't use anything, so first we must know the real number of who are practising: a person can do more things.
For doing this, is better use a three-circles graphic, but we try to do without it.
So
- 16 pool + gym + track, and this number is sure
- 38 gym + pool, but this number includes the people of 1st point. We must know who do only gym + pool: 38 - 16 = 22
- 31 pool + track, this number also includes people of 1st point, so: only pool + track 31 - 16 = 15
- 33 gym + track, this number also includes people of 1st point, so: only gym + track 33 - 16 = 17
now:
- 67 gym, we must know who use only gym: 67 - 16 (gym + pool + track) - 22 (gym + pool) - 17 (gym + track) = 12
- 62 pool, we must know who use only pool: 62 - 16 (gym + pool + track) - 22 (gym + pool) - 15 (pool + track) = 9
- 56 track, we must know who use only track: 56 - 16 (gym + pool + track) - 15 (pool + track) - 17 (gym + track) = 8
now we must now who do some facility: let's sum all
16 + 22 + 15 + 17 + 12 + 9 + 8 = 99
99/100 practise something
So only 1/100 doesn't use nothing
The probability is 1%
