Oftentimes, the College Board and ACT will test a concept differently than it is tested in the classroom. For example, given this systems question:
If 2x + 5y = 1 and 5x - 3y = 8, what is the value of 3x-8y ?
Most students would use linear combination to make either the x-coefficient or the y-coefficient the same in order to get rid of the x or the y, when a student just needs to line the 2 equations up and subtract:
5x - 3y = 8
-(2x + 5y = 1)
3x - 8y = 7 Ans.: 7