The sum of two numbers is 30. The first number is twice the second number. What are the numbers?
Let the numbers be x and y.
We'll write the equation equivalent to the statement: The sum of the numbers is 30.
x + y = 30
Let the 1st number be x.
Since the 1st number is twice the second, we'll re-write the equation above:
2y + y = 30
3y = 30
y = 10
x = 30 - y => x = 30-10
x = 20
The requested numbers are x = 20 and y = 10.