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???

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

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.)

[ 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