Question

How many litres of a 90% solution of concentrated acid needs to be mixed with a 75% solution of concentrated acid to get a 30 l solution of 78% concentrated acid? op 1: 24 l op 2: 22.5 l op 3: 6 l op 4: 17.5 l?

Answer 1

Answer: -

Option 3 : 6 L

Explanation: -

Let the amount of 90% solution of concentrated acid added be A.

Let the amount of 75% solution of concentrated acid added be B.

Since total volume must be 30 L,

A + B = 30                                                              .......equation 1

Amount of acid in A L of 90% concentrated acid = A x $\frac{90}{100}$

                        = 0.9 A

Amount of acid in B L of 75% concentrated acid = A x $\frac{75}{100}$

                        = 0.75 B

Amount of acid in 30 L of 90% concentrated acid = 30 x $\frac{78}{100}$

                        = 23.4

Thus 0.9 A + 0.75 B = 23.4                                          ....equation 2

By multiplying equation 1 by 0.9 we get

0.9 A + 0.9 B = 27                                                         .....equation 3

Subtracting equation 2 from 3

We get 0.15 B = 3.6

B = $\frac{3.6}{0.15}$ = 24

From equation 1

A + B = 30

A = 30 - B

  = 30 - 24

 = 6

Thus 6 litres of a 90% solution of concentrated acid needs to be mixed with a 75% solution of concentrated acid to get a 30 l solution of 78% concentrated acid.

Answer 2

Answer:

Explanation:if the number is divisible by 16