Answer:
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Step-by-step explanation:
1. Check the tree diagram in the picture attached.
2. The blue segment represents "on time"
The red segment represents "not on time"
3. blue - blue - red represents the case 1st on time, 2nd on time, 3rd not on time.
the combined probability is 90/100*90/100*10/100=9/10*9/10*1/10=99/1000=0.099
4. Remark with a tree diagram we can tell anything asked about the probability of an experiment.
You just need to plug those expressions inside the formula: it doesn't matter if they're expressions involving a variable instead of plain numbers: the formula becomes

If you want, you can simplify it by expanding the square and then multiply the two parenthesis:

For this case we have to:
Given the quadratic equation of the form:

The roots are given by:

If we have: 
We can rewrite it in the following way:

Where:

Where we have:



By definition: 




Thus, the roots are given by imaginary numbers:

Answer:
