1) Expression given: 20a+15ab+24b
2) Greates common factor GFC:
i) Coefficients:
20 = 2² × 5 × 1
15 = 3 × 5 × 1
24 = 2³ × 8 × 1
GCF = common numbers raised to the lower power = 1.
ii) Letters:
a
ab
b
Since, none letter is in the three terms, then there is not common letter as GFC.
iii) Conclusion the GCF is 1.
3) Let's see every option of the list:
i) The factors common to 20a and 15ab are 1, 5, a, and b.
FALSE: becasue b is not in 20a.
ii) The factors common to 20a and 15ab are 1, 5, and a.
TRUE: 1, 5, and a are in contained in both terms.
iii) The factors common to 15ab and 24b are 1, 3, a, and b.
FALSE: a is not in 24b
iv) The factors common to 15ab and 24b are 1, 3, and b.
TRUE: 1, 3, and b are contained in both terms.
v) The factors common to 20a and 24b are 1, 2, 4, a, and b.
FALSE: a is not in 24b and b is not in 20a.
vi) The factors common to 20a and 24b are 1, 2, and 4.
TRUE: 1, 2, and 4 are contained in both terms.
vii) The GCF of the expression is ab.
FALSE: as seen above ab is not a common factor.
viii) The GCF of the expression is 1
TRUE: it was proved above.