C) \( \frac{9}{10}+\frac{99}{100} \)

Let’s combine these fractions! To add \( \frac{9}{10} \) and \( \frac{99}{100} \), we first find a common denominator. The least common multiple of 10 and 100 is 100. So, we convert \( \frac{9}{10} \) to have a denominator of 100. This gives us \( \frac{9 \times 10}{10 \times 10} = \frac{90}{100} \). Now we can add: \( \frac{90}{100} + \frac{99}{100} = \frac{189}{100} \). This simplifies to \( 1.89 \) or \( 1 \frac{89}{100} \) in mixed number form! Want to impress your friends? Explain how fractions like these are everywhere in real life! Whether you're splitting a pizza (yes, please!) or figuring out discounts while shopping, adding fractions helps us navigate daily decisions. Understanding them is like having a superpower in the world of numbers! Lastly, a common mistake when adding fractions is forgetting to find a common denominator first. It's like trying to mix apples and oranges without making sure they're both the same size first – they just won't fit together nicely! Always double-check your denominators before diving into addition. Happy calculating!