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

 

so im confued because  adding 6 on bothsides equals .75

and adding 7 on both = .8???

 Apr 5, 2019
 #1
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+1

[+5 - 3] / [+8 - 3] =2 / 5 = 0.4

 Apr 5, 2019
 #2
avatar+27653 
+1

Try adding a negative number, and note that 0.4 is 2/5.

 

Alternatively, solve (5+x)/(8+x) = 0.4 for x.

 

(Too late! Guest has already supplied the answer.)

 Apr 5, 2019
edited by Alan  Apr 5, 2019
 #3
avatar+99237 
+1

[ 5 +x]           4

______  =  ____     cross-multiply

[8 + x]          10 

 

10 [ 5 + x]  =  4 [ 8 + x]      simplify

 

50 + 10x  =  32 + 4x          subtract 4x, 50  from both sides

 

6x =  - 18                   divide both sides by 6

 

x =  - 3

 

 

cool cool cool

 Apr 5, 2019

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