A sample of a radioactive isotope had an initial mass of 120 mg in the year 2010 and decays exponentially over time. A measurement in the year 2015 found that the
sample's mass had decayed to 50 mg. What would be the expected mass of the sample
in the year 2018, to the nearest whole number?

Hi. you've asked an incomplete question. However, I provided some explanation about algebraic expressions and numerical expression.

Step-by-step explanation:

First, we may wonder: What is a numerical expression? In simple words, they are mathematical expressions that contain numbers and operations (like +, -, ÷, ×).

For example, 7+70, 90-10, 60÷10, 5×4 are numerical expressions.

While an algebraic expression on the other hand is a mathematical expression that contains at least one variable.

Variables are letters or symbols (like x, y, p, q, etc) that represent an unknown number or value in a mathematical expression.

For example, 7x+70, 90y-10 are algebraic expressions since they contain at least one variable.