Shortcut Trick
Solve for x, y, z in terms of a using basic elimination: we get x = 3a, y = 6 − 4a, and z = 6 − 5a.
The difference between y and z is y − z = (6 − 4a) − (6 − 5a) = a.
For x, y, z to be three consecutive integers, the difference between any two must be an integer and cannot exceed 2.
From the given options, substituting a = 1 gives x = 3, y = 2, z = 1, which perfectly forms a set of three consecutive integers (1, 2, 3).
∴ The correct answer is 1.
Alternate Method
Given:
x − y + z = 2a ... (i)
x + 4y − 2z = 12 − 3a ... (ii)
2x − 3y + 4z = 6 − 2a ... (iii)
Calculations:
⇒ Multiply equation (i) by 2 and add to equation (ii):
⇒ 2(x − y + z) + (x + 4y − 2z) = 4a + 12 − 3a
⇒ 2x − 2y + 2z + x + 4y − 2z = a + 12
⇒ 3x + 2y = a + 12 ... (iv)
⇒ Multiply equation (i) by 4 and subtract equation (iii):
⇒ 4(x − y + z) − (2x − 3y + 4z) = 8a − (6 − 2a)
⇒ 4x − 4y + 4z − 2x + 3y − 4z = 8a − 6 + 2a
⇒ 2x − y = 10a − 6 ... (v)
⇒ Multiply equation (v) by 2 and add to equation (iv):
⇒ 2(2x − y) + (3x + 2y) = 2(10a − 6) + (a + 12)
⇒ 4x − 2y + 3x + 2y = 20a − 12 + a + 12
⇒ 7x = 21a
⇒ x = 3a
⇒ Substitute x = 3a into equation (v):
⇒ 2(3a) − y = 10a − 6
⇒ 6a − y = 10a − 6
⇒ y = 6 − 4a
⇒ Substitute x = 3a and y = 6 − 4a into equation (i):
⇒ 3a − (6 − 4a) + z = 2a
⇒ 7a − 6 + z = 2a
⇒ z = 6 − 5a
⇒ Since x, y, and z are consecutive integers, let us check the difference between them.
⇒ y − z = (6 − 4a) − (6 − 5a) = a
⇒ For the variables to be consecutive integers, the absolute difference between any two cannot exceed 2.
⇒ Substitute a = 1 from the given options:
⇒ x = 3(1) = 3
⇒ y = 6 − 4(1) = 2
⇒ z = 6 − 5(1) = 1
⇒ The values 1, 2, and 3 correctly form a set of three consecutive integers.
∴ The correct answer is 1.
Additional Information
System of Linear Equations
A system of three linear equations can be solved by progressively eliminating variables until a single variable remains. Substitution and coefficient matching (addition/subtraction) are the most common algebraic methods.
Consecutive Integers
A sequence of integers where each number is exactly 1 more than the previous number. The maximum difference between the largest and the smallest number in a set of three consecutive integers is exactly 2.