Add. Put your answer in simplest form. \[ -\frac{1}{10}+\frac{9}{25} \] $-\frac{1}{10}+\frac{9}{25}=$ (Type a fraction in lowest terms.)

Step 1 ：Convert the first fraction \(-\frac{1}{10}\) to have a denominator of 50 by multiplying both the numerator and the denominator by 5. This gives us \(-\frac{5}{50}\).

Step 2 ：Convert the second fraction \(\frac{9}{25}\) to have a denominator of 50 by multiplying both the numerator and the denominator by 2. This gives us \(\frac{18}{50}\).

Step 3 ：Add the two fractions \(-\frac{5}{50} + \frac{18}{50}\) to get \(\frac{13}{50}\).

Step 4 ：The fraction \(\frac{13}{50}\) is already in its simplest form, so there is no need to simplify it further.

Step 5 ：Final Answer: \(\boxed{\frac{13}{50}}\)