Question

A digital camera for $249.99 at 4% sales tax

Answer 1

i'll round the 249.99 to 250 for simplicity
250*1.04=260 or 259.9975 if you want to be technical

Answer 2

First, change the 4% into a decimal. Once thats changed, it will be 1.04
Multiply 1.04 by the amount of the cost, to get your answer.
But, to make this easier, and to not go through more work, lets round your money amount to $250
Now, all you have to do is multiply.
$250 · 1.04 ≈ $260
So, your answer for $250 with 4% (1.04) percent sales tax would be a grand total of:
$260
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-Hope this helped :)