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avatar+164 

If I add 20% to a number and end with 90, what number did I start with?

 Apr 2, 2018
 #1
avatar+103123 
+2

N  + .20N   = 90  simplify

 

1.20N   = 90       divide both sides by 1.20

 

N  = 75  = the number you started with

 

Verify

 

75  +  20%  of 75  =

 

75  +  (20/100)*75  =

 

75  +  (1/5)*75  =

 

75  +  15  =

 

90  ....

 

 

cool cool cool

 Apr 2, 2018
 #2
avatar+4322 
+1

120%=90

1%=90/120

100%=90/120*100=75! Just like what CPhill got!

 Apr 2, 2018

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