How many gallons of a 60% solution should Christine add to 30 gallons of a 10% solution to produce a 40% solution?

Being there are rules about homework...

What do YOU think the answer should be first... and we'll help you with mistakes you may make...

The site rules for homework.

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The product of concentration and volume is what you have to look for.

For example, let A, B and C be the concentrations of solutions a, b and c respectively.

Aa + Bb = Cc

Apply this to your problem now.

You know A, B and C as concentrations and you know b as volume. Also remember that volumes add too!

So, a + b = c

Give it a try!