This is your bread-and-butter technique. When you have an expression like 5a − 3b and you’re told a = 7 and b = 2, you literally substitute the numbers in. It’s like replacing the actor in a movie—you keep the script, but update the face. A fun cultural parallel? Remember in Friends when Rachel kept trying to replace the trifle recipe? That was a substitution disaster. Here, it’s flawless.
Practical tip: always write the variables in parentheses before plugging in numbers. For instance, 5(a) − 3(b). This small habit prevents those silly arithmetic errors that make you want to flip the table. Parentheses are your safety net—even mathletes use them.
