A restaurant bill is $68. A customer wants to leave an 18% tip. What is the total amount paid, including the tip?

The tip is $18\%$ of the bill: $68(0.18)=12.24$ dollars. The total paid is the bill plus the tip: $68+12.24=80.24$ dollars, choice J. Equivalently, multiply by $1.18$: $68(1.18)=80.24$. Choice F ($12.24) is only the tip, not the total. Choice G ($68.18) adds $0.18$ dollars rather than $18\%$. Choice H ($79.44) comes from a miscalculated tip of about $11.44, which is $16.8\%$ and not $18\%$. Always check that the tip is a sensible fraction of the bill: $10\%$ is $6.80, so $18\%$ should be a little under double that.