90%acid solution (90%pure acid &10%water) and 97% acid solution are mixed to obtain 21litres of 95% acid solution. How many litres of each solution are mixed

Consider the solutions to be A and B respectively

Let X litres of A be mixed with Y litres of B

Given that,

X + Y = 21 (equ.1)

Quantity of acid present in X litres of A = 90% of X

(90/100) X

9X/10

Quantity of acid in Y litres of B = 97% of Y

(97/100)Y

97Y/100

Quantity of acid in 21l of A + B = 95% of 21l

= (95/100)25

= (399/20)

(9X/10) + (97Y/100) = 399/20

90X + 97Y = 1995 (equ.2)

Multiplying equ 1 by 90

90X + 90Y = 1890 (equ.3)

Subtracting equ 3 from 2, we get Y = 15

Substituing Y in equ.1, we get X = 6

Therefore, 6 litres of 90% solution is mixed with 15 litres of 97% solution.

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