Respuesta :

hdjd1
First u can do 3+4+5 then 5+4+3
sheeda1st
way one: put the biggest number in your head in this case 5 then count up 4 then 3 more so you get 12 

way 2: draw 3 tally marks then 4 more then 5 more then count them all together to get the sum 12

hope this helped:)

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