The student council bought two various kinds of candy for the school fair. They purchased 40 pounds of candy at $2.15 per pound and x pounds at $1.90 per pound. What is the total number of pounds they bought if the total amount of money spent on candy was $158.20?

Let x = the amount of candy at $1.90 per pound. Let y = the total number of pounds of candy purchased. If it is known in which there are 40 pounds of candy at $2.15 per pound, after that the total amount of candy can be expressed as y = x + 40. Use the equation 1.90x + 2.15(40) = $158.20 because the total amount of money spent was $158.20. Multiply on the left side: 1.90x + 86 = 158.20. Subtract 86 from both sides: 1.90x + 86 - 86 = 158.20 - 86. Simplify: 1.90x= 72.20. Divide both sides by 1.90: 1.90x/1.90 = 72.20/1.90; so, x = 38 pounds, that is the amount of candy in which costs $1.90 per pound. Thus, the total amount of candy is 38 + 40, that is 78 pounds.