Answer:Regrouping the numbers in the following problems,by putting the numbers that add up to 10 or a multiple of 10 ,
a.) 2+9+8=2+8+9 (commutative property in addition)
=10+9=19(associative property)
b.)3 + 5 + 4 + 7 =3+5+7+4=3+7+5+4 (commutative property in addition)
=10+9=19
c.)4 + 2 + 16=4+16+2(commutative property in addition)
=20+2=22(associative property)
d.) 31 + 4 + 9=31+9+4(commutative property in addition)
=40+4=44(associative property)