Question 174604
Let S = the number of single-dip cones sold and D = the number of double-dip cones sold.
From the problem description, you can write:
1) S+D = 500 "...500 cones were sold..."  Rewrite this equation as S = 500-D and substitute into equation 2) for S.
2) 1.75(S) + 2.25(D) = 900 "...for $900."
2a) 1.75(500-D)+2.25(D) = 900 Simplify this and solve for D.
2b) 875-1.75D+2.25D = 900 Subtract $875 from both sides.
2c) -1.75D+2.25D = 25 Combine like-terms.
0.5D = 25 Divide both sides by 0.5
D = 50 This is the number of double-dip cones sold.
S = 500-D
S = 500-50
S = 450 This is the number of single-dip cones sold.