Math
posted by chaya .
The variable d represents the cost of a customer's meal, in dollar. The following expression represents the amount paid, including tax.
d + 0.18d
F. The cost plus eighteen percent of the cost
G. the cost minus eighteen percent of the cost
H. the cost plus eight percent of the cost
J. The cost plus one hundred eighteen percent of the cost
I think the answer is F.
I really don't get this question
A merchant spend $92 to buy a calculator
then the merchant sold it with a 21% markup. Katherine used her calculator and found the amount of the markup to be $9.
Explain how you can use estimation to check the reasonableness of Katherine's
calculation
part B
Without doing calculation, tell whether or not Katherine's calculation is reasonable explain your answer
I really don't get this question can u help me

Your first answer is right.
If you take 20% of 100, you'll get $20. It looks like Katherine's estimate is way off. 
Another way to approach this problem is to look the relationship between 9 and 90. 9 is 10% of 90, right?

thanks your great

You're very welcome. :)