How many acute angles can a quadrilateral have?

##0##, ##1##, ##2## or ##3##

The sum of the internal angles of a quadrilateral is ##360^@##.

Hence the maximum number of acute angles a quadrilateral can have is ##3##, since the ##4##th angle will be forced to be greater than ##90^@##.

In the following picture, the red square has no acute angles, the green kite has one acute angle, the blue rhombus has two and the gold kite has three.