Case 1: Probabilities cannot add up to a number greater (or less) than 1. This would mean there is greater than a 100% chance of something happening which just doesn't make sense. 0.4 + 0.4 + 0.3 = 1,1
Case 2: You cannot have a negative probability. That is claiming that there is a -10% chance of an event happening, there is at the very least a 0%. Despite them "adding" up to 1, the negative probability makes no sense.
Hope I helped!
Answer:

Step-by-step explanation:

Cross multiply

Divide by 39

Y+3=1/4x-1/4
0.25x-y=3-0.25
0.25x-y=2.75
Answer:
- 1/24
Step-by-step explanation:
Keep multiplying by -1/2 to find the 'next' term
1/12 * - 1/2 = - 1/24