Answer:
70 milliliters
Step-by-step explanation:
Let x be the 51% solution and y be the 69% solutions,
Since, the solution after combining them = 180 milliliters
⇒ x + y = 180 -----(1),
Also, final solution is of 62%,
That is,
51% of x + 69% of y = 62% of 180
0.51x + 0.69y = 0.62 × 180
⇒ 0.51x + 0.69y = 111.6,
⇒ 51x + 69y = 11160 -----(2),
Equation (2) - 69 × equation (1),
We get,
-18x = -1260
⇒ x = 70
Hence, 70 milliliters of the 51% solution should she use.
