Question 38·Medium·Linear Inequalities in One or Two Variables
Which of the following ordered pairs is a solution to the system of inequalities above?
For SAT questions asking which ordered pair satisfies a system of linear inequalities, the fastest method is usually to plug in the answer choices directly instead of solving algebraically or graphing from scratch. Substitute each pair into the first inequality and quickly eliminate any that fail, paying attention to strict vs. non-strict symbols like versus . Then check any remaining candidate(s) in the second inequality. This plug-in-and-eliminate approach is quick, minimizes algebra, and reduces the chance of graphing errors under time pressure.
Hints
Think about what a solution to a system is
A point is a solution to a system of inequalities only if it makes all of the inequalities true at the same time. How could you check that for a specific ordered pair?
Start with the first inequality
For each answer choice, substitute the - and -values into . Which options make the left side less than 6, and which do not?
Use the inequality symbols carefully
Pay close attention to the difference between and . A result equal to 6 does not satisfy , but a result equal to does satisfy .
Check any remaining candidates in the second inequality
Once you know which ordered pairs (if any) work for , test those in by computing and comparing it with .
Desmos Guide
Graph the inequalities
In Desmos, enter the inequalities as two separate expressions:
2x + 3y < 6y >= x - 4
Desmos will shade the region for each inequality; the solution set to the system is where the shaded regions overlap.
Plot the answer choices as points
Add each answer choice as a point in Desmos by typing them on separate lines, for example:
(0, 2)(2, -1)(1, 3)(4, 0)
Each will appear as a dot on the graph.
Identify the solution visually
Look for which of the four plotted points lies inside the overlapping shaded region (not just on a region that only one inequality shades). The point that lies in this common region corresponds to the correct answer.
Step-by-step Explanation
Understand what a solution to a system means
A solution to the system
is an pair that makes both inequalities true at the same time. We can test each answer choice by substituting its - and -values into each inequality.
Use the first inequality to filter the choices
Check for each option:
- For : , and is false, so this pair fails the first inequality.
- For : , and is true, so this pair passes the first inequality.
- For : , and is false, so this pair fails the first inequality.
- For : , and is false, so this pair fails the first inequality.
Only one of the four choices makes true; now we must see if that same choice also satisfies the second inequality .
Check the remaining candidate in the second inequality
Take the only pair that satisfied and test it in :
- For : here and .
- Compute : .
- Compare and : is true.
So satisfies both and . Therefore, the solution to the system among the answer choices is .