Josiah went to the local barber to get his hair cut. It cost $18 for the haircut. Josiah tipped the barber 15%. What was the total cost of the haircut including the tip?

2 Answers
Mar 4, 2016

Total cost is $20.70.

Explanation:

Firstly, we must find the cost of the tip. To do this, we need to find 15% of $18. 15% means 15 per 100 (aka: 0.15). 'Of' in mathematics means multiplication. So..

0.15*18=$2.700.1518=$2.70

Now that we know the cost of the tip, we just need to add it to the cost of the haircut.

18+2.70=$20.7018+2.70=$20.70 (total cost of haircut & tip)

And that's your final answer!

Mar 4, 2016

Another approach

$20.70$20.70

Explanation:

color(Red)(115/100xx$18=$20.70)115100×$18=$20.70

'~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
color(green)("Idea behind the calculation method")Idea behind the calculation method

color(blue)("Concept 1")Concept 1

Percent is parts of a hundred. Basically it is a fraction where the denominator is fixed at 100.

So another way of writing 15% is 15/10015100

So 15% of some quantity is the same as 15/100xx" some quantity"15100× some quantity

'~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

color(blue)("Concept 2")Concept 2

Multiply any count by 1 and you do not change the value.

This is because, in words, you are saying you have 1 of them

So 1xx "something"1×something is saying you have 1 of it

color(brown)("But 1 can be written in many ways, say, "100/100)But 1 can be written in many ways, say, 100100

The cut and tip is all of the $18 (1 of it) and 15/10015100 parts of it more

So in fact you are paying (100/100 + 15/100)xx$18(100100+15100)×$18

So you are paying 115/100xx$18 = $20.70115100×$18=$20.70
'~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
color(blue)("Compare to an another method")Compare to an another method

$18+(15/100 xx$18) = $18+$2.70$18+(15100×$18)=$18+$2.70

=$20.70=$20.70