There are $190$ people on the beach. $110$ are wearing sunglasses, $70$ are wearing bathing suits, and $95$ are wearing a hat. Everyone is wearing at least one of these items. $30$ are wearing both bathing suits and sunglasses. $25$ are wearing both bathing suits and a hat. $40$ are wearing both sunglasses and a hat. How many people are wearing all three items?
review inclusion-exclusion principle. You want x such that
110+70+95 - (30+25+40) + x = 190
and lose the useless $$ signs, ok?