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Andy’s average driving speed for a 4-hour trip was 45 miles per hour. During the first 3 hours he drove 40 miles per hour. What was his average speed for the last hour of his trip?

Sagot :

Shinalcantaraviz
the average speed is given as:
[tex]v _{average} = \frac{v_1 + v_2 + v_3 + v_4}{t} [/tex]
where v average in this problem is 45mph  
         v1 = 40mph
         v2 = 40mph
         v3 = 40mph
          t = 4hours
you are asked to find v4
by substituting the given values you'll have:
[tex]45 = \frac{40+40+40+v_4}{4} [/tex]
cross multiply 4 and add the values at the right side
180 = 120 + v4
v4 = 180 - 120
v4 = 60mph