Final answer:
The numerical expression for 'the sum of 4 multiplied by 5 and a multiplied by b' is 4 × 5 + a × b, which uses basic algebraic principles.
Step-by-step explanation:
The numerical expression for the statement is 4 × 5 + a × b. This expression represents the sum of two products: the product of 4 and 5, and the product of the variables a and b. According to the commutative property of addition, which states that A + B = B + A, the order of addition does not affect the sum. Additionally, this question involves an understanding of basic algebra and the properties of operations.