Question 1129855
x = the number of ounces of the 70% solution.
y = the numberof ounces of the 95% solution.


x + y = 70
.7 * x + .95 * y = .9 * (x + y)


since x + y = 70, the second equation becomes:


.7 * x + .95 * y = .9 * 70 = 63


your two equations that need to be solved simultaneously are:


x + y = 70
.7 * x + .95 * y = 63


multiply both sides of the first equation by .7 and leave the second equation as is to get:


.7 * x + .7 * y = 49
.7 * x + .95 * y = 63


subtract the first equation from the second to get .25 * y = 14


solve for y to get y = 56


from x + y = 70, solve for x to get x = 14


your solution is x = 14 and y = 56.
that means that you need 14 ounces of the 70% solution and 56 ounces of the 95% solution to get 70 ounces of a 90% solution.


.7 * 14 + .95 * 56 = 63
63 / 70 = .9 = 90%