What number, when added to the numerator and to the denominator of #5/8#, results in a fraction whose value is 0.4?

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Answer 1 · 2018-04-28T22:00:20

#n=-3#

let #n# be that number

#(5+n)/(8+n)=0.4#

Many ways to solve, I prefer turning it into a fraction:

#(5+n)/(8+n)=2/5#

#2(8+n)=5(5+n)#

#16+2n= 25+5n#

#-9=3n#

#n=-3#

Another way:
#(5+n)/(8+n)=0.4#

#5+n=0.4(8+n)#

#5+n= 3.2+0.4n#

#1.8= -0.6n#

#n=-3#