Why Bother Asking?
We think the OP is complaining about nothing. 99 + 99 is not a simple math equation, especially for those that don’t have a first-class honor’s degree in mathematics or ever worked as a finance assistant. However, if you do seek math advice from someone with such credentials, maybe you should listen to what they have to say.
Look, every English-speaking person on the planet learned the alphabet when they were still in preschool or kindergarten. That doesn’t mean they always know whether the letter S comes before or after R. Double-checking isn’t always the worst thing in the world, though we do understand the OP’s frustration.