\[\frac{1}{\sqrt{36} + \sqrt{37}} + \frac{1}{\sqrt{37} + \sqrt{38}} + \ldots + \frac{1}{\sqrt{48} + \sqrt{49}} =\]
\[= \frac{\sqrt{36} - \sqrt{37}}{36 - 37} + \frac{\sqrt{37} - \sqrt{38}}{37 - 38} + \ldots + \frac{\sqrt{48} - \sqrt{49}}{48 - 49} =\]
\[= \frac{\sqrt{36} - \sqrt{37} + \sqrt{37} - \sqrt{38} + \ldots + \sqrt{48} - \sqrt{49}}{- 1} =\]
\[= \frac{\sqrt{36} - \sqrt{49}}{- 1} = \frac{6 - 7}{- 1} = 1.\ \]