Question

A solution is prepared by addition of 10 g salt in
100 g water. To make the concentration of the
solution 15% (w/w), the amount of salt added to the
solution is approximately
(1) 5.8 g
(2) 5.0 g
(3) 6.9 g
(4) 7.6 g

Answer 1

(4) 7.6g

the equation happens to be 

(10 + x)/(110+x) = 0.15
therefore 10 + x = 16.5 + 0.15x
therefore x - 0.15x = 6.5
therefore .85x = 6.5
therefore x = 7.6 (approx)

Answer 2

Answer:

7.6g

Explanation:

10/110×100=9.09%

x/100+x×100=15

100x=1500+15x

x=17.6g

therefore 7.6 g is to be added more