Respuesta :
The postages that can be formed using just 3-cent and 10-cent stamps are linear combinations 3x + 10y.
How to prove by using induction?
Let P(n) = postage of n cents
n = 18
P(18) is true because 18 cents can be formed by using six 3 cent stamps.
By using the principle of mathematical induction, P(n) is true for all positive integers n.
Also, by using strong induction, P(n) will be postage of n cents that are formed by using 3 cent and 10 cent stamps.
n = 18, 19, and 20.
P(18) is true because 18 cents can be formed by using six 3-cent stamps.
P(19) is true because 19 cents can be formed by using one 10-cent stamp and there 3-cent stamps.
P(20) is true because 2 10-cent stamps can be used.
In conclusion, the principle of strong induction is true for all positive integers n.
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