Several biology students are counting kernels in an ear of corn. they count a total of 420 kernels: 242 purple wrinkled, 84 purple smooth, 70 yellow wrinkled, and 24 yellow smooth. what is the ratio of kernel phenotype in this case? a) 3: 2: 2: 1 b) 8: : 4: 2: 1 c) 9: 3: 3: 1 d) 24: 8: 7: 2

The answer is C) 9:3:3:1

This looks like a dihybrid cross where the expected phenotypic ratio is 9:3:3:1. However, in nature, the numbers cannot be absolut. Let's check it out:
242 purple wrinkled
84 purple smooth
70 yellow wrinkled
24 yellow smooth

Divide all by the smallest number:
242 purple wrinkled / 24
84 purple smooth / 24
70 yellow wrinkled / 24
24 yellow smooth / 24

We have 
10.1 purple wrinkled which is near to 9
3.5 purple smooth which is near to 3
2.9 yellow wrinkled which is near to 3
1 yellow smooth

Compound light microscope