Composite Samples of Milk. 171 



Methods of calculating average percentages. 



*56. 2X100 

 1187 



=4.73. 



+49.8X100 

 1187 



197. The figures given in the table show that when 

 the different lots of milk vary in test and weight, as in 

 the first case, the correct average test of the 1187 Ibs. 

 of milk is not found by dividing the sum of these tests 

 by five, which would give 4.14 per cent. ; but the per- 

 centage which 56.2 (the total amount of fat in the 

 mixed milk) is of 1187 (the total amount of milk), is 

 4.73, and this is the correct average test of the mixed 

 milk made up of the five different lots. 



In the second case, the variations in both the weights 

 of the different lots of milk and their tests, are com- 

 paratively small, and both methods of calculation give 

 therefore practically the same average test; but also in 

 this case, the correct average test is found by dividing 

 the total amount of fat by the total quantity of milk, 

 making 4.22 per cent., instead of 4.20 per cent., wnich is 



