When combining like terms, which of the following is incorrect?

• A. Combining 3m and 2m
• B. Combining 5a and 5b
• C. Combining 4x² and 6x²
• D. Combining 7p and 3p

Answer: (B)

The choice of combining 5a and 5b is indeed incorrect because these two terms are not like terms. Like terms are those that have the same variable raised to the same power. In this case, 5a involves the variable 'a', while 5b involves the variable 'b'. Since 'a' and 'b' are different variables, they cannot be combined through addition or subtraction.

In contrast, the other options involve combining like terms. For instance, combining 3m and 2m results in 5m, since both terms share the same variable 'm'. Similarly, combining 4x² and 6x² results in 10x², as they both have the same variable x raised to the same exponent. Lastly, when combining 7p and 3p, you obtain 10p, since both terms contain the same variable 'p'. Thus, the correct answer highlights the importance of recognizing like terms in algebraic simplification.