The bill plus a 15% tip

Question

Solve in your head. A meal costs \46. With a 15\% tip, what is the total you pay? Aim: under 8 seconds.

Accepted Answer

First the tip, from blocks: 15\% = 10\% + 5\%. - 10\% of 46 is 4.6. - 5\% is half of that: 2.3. - Tip = 4.6 + 2.3 = 6.9. Then add it back to the bill (this is the part candidates forget: the question wants the total, not the tip): 46 + 6.9 = 52.9. Takeaway. A "total with tip" is two moves: compute the percentage from 10\% and 5\% blocks, then add it to the original. A handy shortcut for the whole thing: a 15\% total is 1.15	imes the bill, so 46 	imes 1.15 = 52.9 directly.

The bill plus a 15% tip

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