Let P (n) be the statement that a postage of n cents can be formed using just 4-cent stamps and 7-cent stamps. The goal is to show, using strong induction, that P (n) is true for all integers n ≥ 18.

Complete Question

Let P (n) be the statement that a postage of n cents can be formed using just 4-cent stamps and 7-cent stamps. The parts of this exercise outline a strong induction proof that P (n) is true for n ≥ 18.

Show statements P (18), P (19), P (20), and P (21) are true, completing the basis step of the proof.

Answer:

P (18) is true

P (19) is true

P (20) is true

P (21) is true

Step-by-step explanation:

a. When n = 18

18 cents can be formed using two 7cents and one 4cents

i. e. 2 * 7 + 4 = 18

So, P (18) is true

b. When n = 19

19 cents can be formed using one 7cents and three 4cents

i. e. 1 * 7 + 3 * 4 = 19

So, P (19) is true

c. When n = 20

18 cents can be formed using five 4cents

i. e. 5 * 4 = 20

So, P (20) is true

d. When n = 21

18 cents can be formed using three 7cents

i. e. 3 * 7 = 21

So, P (21) is true