Recall that the two acute angles of a right triangle add up to 90 degrees.
Let s be the measure (in degrees) of the smallest angle of the given right triangle, then we can set the following equation:
[tex]s+40+s=90.[/tex]Adding like terms we get:
[tex]2s+40=90.[/tex]Subtracting 40 from the above result we get:
[tex]\begin{gathered} 2s+40-40=90-40, \\ 2s=50. \end{gathered}[/tex]Dividing the above result by 2 we get:
[tex]\begin{gathered} \frac{2s}{2}=\frac{50}{2}, \\ s=25. \end{gathered}[/tex]Therefore the measure of the smallest angle is 25º.
Answer: 25º.