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=$2.70#

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

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

And that's your final answer!

Mar 4, 2016

Another approach

#$20.70#

Explanation:

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

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

#color(blue)("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 #15/100#

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

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

#color(blue)("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"# is saying you have 1 of it

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

The cut and tip is all of the $18 (1 of it) and #15/100# parts of it more

So in fact you are paying #(100/100 + 15/100)xx$18#

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

#$18+(15/100 xx$18) = $18+$2.70#

#=$20.70#