Answer:
Given that
                                                                  1
John can run 100 meters dash in 16    --------- seconds .
                                                                   5
Savanna 's time is 19.8 seconds .
Here we have John time in mixed fraction and Savanna's time in decimal .
Converting mixed fraction into improper .
      1                      16 * 5     +  1                 80 + 1                 81
16  --------    =     ---------------------------    =   -------------- =   - -----------
     5                           5                                  5                      5
Thus we got John time as 81 /5 seconds .
Converting Savanna's time in fraction , we get
 19 8
----------  seconds .
   10  
We have two fractions with different denominator .
One is having denominator 5 and another is having denominator 10 .
We need to make the denominator same of both the fraction .
We need to make denominator 10 .
Multiply John fraction by 2 in both numerator and denominator by 2 to make denominator 10 .
81 * 2               162
----------  =      ------------ seconds .
5 *  2                   10
John is taking less time than Savanna . Thus John is faster .
Difference
198          162            36
-------  -     -------     =  ------- seconds  
10              10              10
Thus John is faster by  (36/10 ) seconds  =  3.6 seconds.
Step-by-step explanation:
Given that
                                                                  1
John can run 100 meters dash in 16    --------- seconds .
                                                                   5
Savanna 's time is 19.8 seconds .
Here we have John time in mixed fraction and Savanna's time in decimal .
Converting mixed fraction into improper .
      1                      16 * 5     +  1                 80 + 1                 81
16  --------    =     ---------------------------    =   -------------- =   - -----------
     5                           5                                  5                      5
Thus we got John time as 81 /5 seconds .
Converting Savanna's time in fraction , we get
 19 8
----------  seconds .
   10  
We have two fractions with different denominator .
One is having denominator 5 and another is having denominator 10 .
We need to make the denominator same of both the fraction .
We need to make denominator 10 .
Multiply John fraction by 2 in both numerator and denominator by 2 to make denominator 10 .
81 * 2               162
----------  =      ------------ seconds .
5 *  2                   10
John is taking less time than Savanna . Thus John is faster .
Difference
198          162            36
-------  -     -------     =  ------- seconds  
10              10              10
Thus John is faster by  (36/10 ) seconds  =  3.6 seconds.