Answer:
126 combinations can be tested.
Step-by-step explanation:
An agriculture researcher wants to test the effect of nine soil additives by adding four at a time to different rows.
We have to find the combination which can be tested.
Combinations formed can be written as [tex]^{9}C_{4}[/tex]
[tex]^{9}C_{4}[/tex] = [tex]\frac{9!}{(4!)(9-4)!}[/tex]
= [tex]\frac{9!}{4!5!}=\frac{9\times 8\times 7\times 6\times 5!}{(4\times 3\times 2\times 1)\times 5!}[/tex]
= [tex]\frac{9\times 8\times 7\times 6}{4\times 3\times 2\times 1}[/tex] = [tex]\frac{3024}{24}=126[/tex]
therefore, 126 combinations can be tested.
