In a survey of 250 business executed 20 said they do not read money fortune for business week while 180 said they read exactly one of these tree and 42 said they read exactly two of them. how many read all three? ​

I think 8 people read three.

Out of 250 business executives, we can cross out the 20 who don't read money fortunes. That leaves us with 230 executives. We can cross out 180 of the 230 because they read only 1, it doesn't mean that part of them reads three. We are left with 50, but because 42 read only 2, only 8 actually reads three.