Algebra 3
3 marks · EasyThe sum of two numbers is 18.
Let the numbers be x and y. Write an equation for their sum.
If their difference is 4, write a second equation for x and y.
Solve the equations to find the values of x and y.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) x + y = 18
(b) x - y = 4
(c) x = 11, y = 7
Common mistakes: Using 18-x instead of y
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Correct equation for the sum: x + y = 18.
B1 (b) · 1 mark · Correct equation for the difference: x - y = 4.
M1A1 (c) · 1 mark · Both correct answers: x = 11, y = 7 (follow-through)
Worked solution
a) The sum: x + y = 18
b) The difference: x - y = 4
c) Add the equations:
2x = 22, so x = 11.
Substitute x = 11 into x + y = 18 to get y = 7.