Respuesta :

4+5=9 because your adding hold up 5 fingers in put 4 more that's 9

⇒4+5

=4+4+1----[5=4+1]

=2 × 4 +1

=8+1

= 9

→4+5

=(5-1)+5

 =5+5-1

 =10-1

 =9

Addition Doubles Fact used

→4+4 =8

or

→5+5=10