Question 904976
from view of solution/acid
x+y=50,
.02*50=.30*x
x=3.33334 acid for 30% acid
Notice we don't show the water here because it has zero % acid
We could have shown the water as .02*50=.30*x+0*y
50-x=46.67 70% water 
check
.30*3.33333333+0*.46.6666667=2*.50
1.00+0.0=1.00
1.=1.0
ok

from view of water
x+y=50
70x+100y=98*50
here we show the 50 ml as 98% water (2% acid) so we have 100% water with 70 per cent water (30 % is acid)
x=3.33333 acid ,   y=46.6667 water
check
0.7*3.33333333+1*46.6666667=0.98*50
2.33333333+46.6666667=49
49.0=49
ok