EXPLANATION
Considering the addition
Write the numbers one under the other, line up the decimal points.
Add trailing zeroes so the numbers have the same length.
1. 7 9
+ 0. 1 6
+ 1 9. 9 0
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Add each columns of digits, starting on the right and working left.
If the sum of a column is more than ten, 'carry' digits to the net column on the left.
Add the digits of the bolded column: 9 + 6 + 0 = 15
0 1. 7 9
+ 0 0. 1 6
+ 1 9. 9 0
----------------
Carry 1 to the column on the left and write 5 in the bolded column:
1
0 1. 7 9
+ 0 0. 1 6
+ 1 9. 9 0
----------------
5
Add the digits of the bolded column: 1 + 7 + 1 + 9 = 18
1
0 1. 7 9
+ 0 0. 1 6
+ 1 9. 9 0
----------------
8 5
Carry 1 on the colum to the left and write 8 in the bolded column:
1 1
0 1. 7 9
+ 0 0. 1 6
+ 1 9. 9 0
----------------
8 5
Place the decimal point in the answer directly below the decimal points in the term:
1 1
0 1. 7 9
+ 0 0. 1 6
+ 1 9. 9 0
----------------
.8 5
Add the digits of the bolded column : 1 + 1 + 0 + 9 = 11
1 1
0 1. 7 9
+ 0 0. 1 6
+ 1 9. 9 0
----------------
.8 5
Carry 1 to the column on the left and write 1 in the bolded column:
1 1 1
0 1. 7 9
+ 0 0. 1 6
+ 1 9. 9 0
----------------
1 .8 5
Add the digits of the bolded column: 1 + 0 + 0 + 1 = 2
1 1 1
0 1. 7 9
+ 0 0. 1 6
+ 1 9. 9 0
----------------
2 1 .8 5
The answer is 21.85