Here I will tell you practical stuff where I have encountered Mathematics in solving some Computing Problems (particularly in Internet domain) :

1. Search Engines uses Vector Calculus for searching data.
2. Matrix Factorization can be used for a lot of stuff like Sentiment Analysis.
3. You need to know Calculus, Summations for figuring out complexity of code that you write.
4. Probability is heavily used in Probabilistic Information Retrieval/Search
5. Naive Bayes Theorem is used in Predictive Analytics.
6. You need to know stuff like hyper plane etc for a concept called SVM which is again used in Machine Learning for solving categorization problems.
7. You need to understand Entropy for doing Natural Language Processing stuff.
8. Latent Semantic Indexing/ Principal Component Analysis used by Search Engines relies heavily on matrix algebra. & so on......