ACT Math · Linear equations and inequalities

Points A, B, and C are collinear, with B between A and C. If AB = 3x+2, BC = 5x-1, and AC = 33, what is BC?

Points AA, BB, and CC are collinear, with BB between AA and CC. If AB=3x+2AB = 3x+2, BC=5x−1BC = 5x-1, and AC=33AC = 33, what is BCBC?

Answer and explanation

Answer: H: 19

Since BB is between AA and CC, the segments add up: AB+BC=ACAB+BC=AC. Then (3x+2)+(5x−1)=33(3x+2)+(5x-1)=33, so 8x+1=338x+1=33, 8x=328x=32, and x=4x=4. The question asks for BCBC, which is 5(4)−1=195(4)-1=19, choice H. Check: AB=3(4)+2=14AB=3(4)+2=14, and 14+19=3314+19=33. Choice F (1414) is the length of ABAB, not BCBC. Choice G (1616) and choice J (2121) come from substituting incorrect values of xx (x=3.4x=3.4 and x=4.4x=4.4 would be needed). Read carefully which segment the question asks for after solving for the variable.

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