A butcher has supplies of lean beef containing 15% fat, and fat trim containing 100% fat. How many kg of lean beef and fat trim are needed to make 50 kg of hamburger containing 25% fat? (round your answers to 1 decimal place.)

Answer 1

This is just like the interest problem.
If there are x kg of 15% fat, then the rest (50-x) is 100% fat. So, just add up all the fat amounts:

.15x + 1.00(50-x) = .25*50