Answer: $195.30
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Step-by-step explanation:
The bill starts off at $150.
Increase this by 8.5% to get 1.085*150 = 162.75
The 1.085 represents an 8.5% increase. Think of it like 100% + 8.5%
Anyways, the $162.75 is the cost before the tip is considered. So we'll increase this by 20% to get
162.75*1.20 = 195.30 which is the final answer
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It doesn't matter if you apply the 20% tip to the bill before tax or after tax. You'll still arrive at the same final answer.
If we applied the 20% tip first, then,
150 jumps to 150*1.20 = 180
Now consider the tax
180 jumps to 1.085*180 = 195.30
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If you wanted to find the grand total (tax plus tip) in one step, then you could write
150*1.085*1.20 = 195.30
The order of multiplication doesn't matter. So that's why we could apply the tax and tip in any order we want.