Make sure you line this problem up correctly and then add
10.47
0.78
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7 plus 8 is 15. Take the 5 down and carry the 1.
4 plus 7 plus 1 is 12. Take the 2 down and carry the 1
0 plus 0 plus 1 is 1
bring the last 1 down
1 1
10.47
0.78
-----------
11.25