Final answer:
Three friends spent $400 in total on teaching aids. By setting up an algebraic equation, we determine that the first person spent $120, the second spent $130, and the third spent $150.
Step-by-step explanation:
The question at hand is a simple algebraic problem. We have three friends who have spent a total of $400 on teaching aids. Let's denote the amount the first person spent as x many. According to the problem, the second person spends x + 10 many and the third person spends (x + 10) + 20 many, which is x + 30 many.
To find out how much each person spent, we set up the equation:
x + (x + 10) + (x + 30) = 400
Combining like terms:
3x + 40 = 400
Subtracting 40 from both sides:
3x = 360
Dividing by 3:
x = 120
Hence, the first person spent $120, the second spent $130 (120 + 10), and the third spent $150 (120 + 30).