30 is 15% of what number?

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Answer 1 · 2016-02-09T12:22:17

#200#

Let #x# be the number:

Then,

#rarr15/100(x)=30#

#rarr3/20(x)=30#

#rarr(3x)/20=30#

#rarr3x=20*30#

#rarr3x=600#

#rarrx=600/3=200#

Answer 2 · 2017-03-23T18:41:29

A lot of detail given in the explanation so that you can see where everything comes from.

30 is 15% of 200

#color(blue)("Preamble")#

You can think of % as a sort of unit of measurement but one that is worth #1/100#

So #15%" "->" "15xx%" "->" "15xx1/100=15/100#
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
#color(blue)("Answering the question")#

Let the unknown value be #x#

Then 15% of #x# = 30

In mathematics the of is rather like multiply, so we have:

#15%xx x =30#

#15xx%xx x = 30#

#15/100x=30#

We need to find the value of #x# so if we can change the value of #15/100# to the value of 1 we will have #x# on its own.

#color(brown)("What you do to one side of the equals you do to the other")#

Multiply both sides by #color(red)(100/15)#

#color(green)(15/100color(red)(xx100/15)xx x " "=" " 30color(red)(xx100/15))#

#1xx x=30/15xx100#

#x=2xx 100#

#x=200#