The mean of two numbers is 49.1. The first number is 18.3. What is the second number

The mean of two numbers is 49.1. The first number is 18.3. What is the second number

We call the second number n. Since the mean is an average, in this case 2 numbers, we have:
(18.3 + n)/2 = 49.1

Cross multiply:
18.3 + n = 98.2

Typing this equation into our search engine, we get:
n = 79.9