Let s = the speed of the slower train in km/hrs+10 = the speed of the faster train in km/hrLet t = time in hrs for the slower train to go 160 kmt-5 = time in hrs for faster train to go 160 km---------------Slower train:(1) 
160=s.t
Faster train:(2) 160=(s+10) .(t-.5)From (1)(1) t=160/s
use the relations given in following screenshot and then use quadratic equation.
 
        
        
        
M = -8 
-15 minus -7 equals -8
        
             
        
        
        
Pythagorean theorem
c2 = a2 + b2
71^2 = 43^2 + b2
5041 = 1849 + b2
3192 = b2
b = 56.5 which is answer choice d
        
             
        
        
        
Answer:
4, see below :)
Step-by-step explanation:
We can rewrite the equation into:
3.5 + 2 - 1.5
First we add 3.5 and 2
3 and 2 are in the ones place so:
5, and then you added the .5
5.5
Then:
5.5 - 1.5
First we subtract the tenths place so:
.5 - .5 = 0
Then the ones:
5 - 1 = 4
 
        
                    
             
        
        
        
<u>10M </u><u>different </u><u>codes </u><u>are possible.</u>
Probability Definition in Math-
- Probability is a measure of the likelihood of an event to occur. Many events cannot be predicted with total certainty. We can predict only the chance of an event to occur i.e. how likely they are to happen, using it.
- Four perspectives on probability are commonly used: Classical, Empirical, Subjective, and Axiomatic.
-  For example, the probability of flipping a coin and it being heads is ½, because there is 1 way of getting a head and the total number of possible outcomes is 2 (a head or tail). We write P(heads) = ½ .
- It’s simple. there are 7 digits, so that would mean you start with 0,000,000 and end with 9,999,999.
-  If the highest digit is 9,999,999 and you add a 1 more to it, you have a total of 10M combinations.
Learn more about probability 
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