There is a row of 15 trees in a garden. Starting from the first tree, a gardener marked every second tree, then, on his way back, he marked the first tree, and then every third tree. How many trees are left without a mark?

Answerthe simplified expression isexplanationthe given expression is,let us deal with the bracket first.the two negatives in the parenthesis will become positive.the expression now becomes,we now expand the parenthesis to get,we group like terms to obtain,this simplifies to,