Answer
Find out the total number of minutes they played using associative property.
To proof
Associative property of addition
This property states that
a + ( b + c) = ( a +b) +c
Where a, b, c are the any numbers.
As given
Sophia Played for 18 minutes and 26 minutes last week should play the piano for 40 minutes last week
let
a = 18 minutes , b = 26 minutes , c = 40 minutes
Total number of minutes sophia played = a + ( b + c) = ( a +b) +c
put the value of a, b,c
Total number of minutes sophia played =18+(26 +40) = (18 +26) + 40
= 18 +66 = 44 + 40
= 84 = 84
satisfy the associative property
Therefore the total number of minutes sophia played be 84 mintues.
Hence proved