a. \( 0,7+\frac{9}{100} \)

To tackle \( 0.7 + \frac{9}{100} \), let's first convert \( 0.7 \) into a fraction. Remember, \( 0.7 \) is equivalent to \( \frac{7}{10} \). Now both numbers can be expressed as fractions: \( \frac{7}{10} + \frac{9}{100} \). To add them, we need a common denominator, which is \( 100 \). Thus, rewrite \( \frac{7}{10} \) as \( \frac{70}{100} \). Now, add: \( \frac{70}{100} + \frac{9}{100} = \frac{79}{100} \). Therefore, \( 0.7 + \frac{9}{100} = 0.79 \). Now let's consider how these decimal and fraction manipulations fit into everyday activities! For instance, shopping often requires us to understand prices and discounts, which sometimes include percentages and decimals. If you spot a sale that offers 7% off an item priced at $100, which translates to $0.07 and $0.09 when calculated, skillfully managing these figures ensures you don’t miss out on the best deals! Learning to master decimal addition and fraction conversions can turn you into a savvy shopper. A common mistake in dealing with decimals and fractions is forgetting to convert one of them to match the other, leading to errors in calculation. Always keep your equivalents in mind: \( 0.5 = \frac{1}{2} \) and \( 0.25 = \frac{1}{4}\) can be crucial in many situations. When you’re adding or comparing them, ensure they have the same denominator to avoid any hiccups in your math, turning potential blunders into smooth sailing!