Question

Ursula wrote the sum 5.815+6.021 as a sum of two mixed numbers.

Answer 1

As the sum of mixed numbers:
5.815 = 5 + 815/1000
6.021 = 6 + 21/100
Therefore
5.815 + 6.021 = 5 + 6 + (815+21)/1000
                       = 11 + 836/1000
                       = 11 + 209/250

Part a.
The sum is $11\, \frac{209}{250}$

Part b.
As the sum of decimals:
   5.815
+ 6.021
  ----------
= 11.836

To compare the two results, evaluate209/250 as a decimal to see whether it is 0.836.

              0.836
       ------------------
250 | 209.000
          2000
          --------
               900
               750
               ----------
               1500
               1500

Because 209/250 = 0.836, the two sums agree.