Sum of 2 field from different table

Hi, I'm new with SQL 2008 and I have one question where I need help.

I have 2 tables (Table1) and (Table2) in same database 

2 tables have similar rows like this :

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Table1:

ID Name Number

1david 3

==============================

Table2:

ID Name Number

1 david 2

==============================

So i want to sum of "Number" from table1 and table2 updated in table1 like this :

Table1 must be :

ID Name Number

1 david 5

How can do this with script ?

Thanks in advance