Mixtures word problems

**If you mix 20kg of type A wheat, which costs €0.60/kg, with 60kg of type B wheat, which costs €0.80/kg, what is the price of the resulting mixture?**

20 Kg. of type A wheat costs 20·0.6 = 12 euros.

60 Kg. of type B wheat costs 50·0.8 = 48 euros.

The resulting mixture is: 80 Kg. of wheat with a price of 60 euros.

Each kg costs:

**1000g of gold which is 90% pure is mixed with an amount of gold which is 75% pure. The purity of the resultant mixture is 85%. What quantity of the gold of 75% purity was added?**

If the purity of the first quantity is 90% then it contains 900g of pure gold.

Name x to the amount of the second mixure, which will contain 0.75x pure golden.

After the mixure, he will have 1000+x gr of metal with 85% purity, that is 0.85(1000+x) gr. of pure golden.

That is

0.85(1000+x)=900 +0.75x ; 850+0.85x=900+0.75x ; 0.1x=50 ; x=500

Solution: 500 gr. were added