Percentages

Question

A scientist mixes water (containing no salt) with a solution that contains 35% salt. she wants to obtain 140 ounces of a mixture that is 30% salt. how many ounces of water and how many ounces of the 35% salt solution should she use?

Answer 1

Jocelyn, I'm going to use the water percentage to solve this. 

 

The first equation is from the information given.

 

w + s = 140

 

Since 100% = 1.00 = 1, and we have 100% solution of water, we don't write 1w, but just w. The solution that's 35% water is 65% water.

 

w + .65s = .70(140)

 

Now, let's solve each for w.

 

w = 140 - s

w = 98 - .65s

 

Since w is equal to two different things, they are equal to each other!

 

140 - s = 98 - .65s

.35s = 42

s = 120

 

w = 140 - 120 = 20

 

So, she needs 20 oz of water and 120 oz of solution.