Let Pn be the statement : any postage of n >= 2 cents can be made of(adsbygoogle = window.adsbygoogle || []).push({});

3-cent and 2-cent stamps. What is wrong with the following proof of

Pn by induction? How can it be fixed without changing the induction

step much?

Base case : 2 = 2 and so P2 is true.

Induction step : Fix some n >=2. Assume that Pk is true for k <= n, we

will prove Pn+1.

Since Pn-1 is true, we know that

n - 1 = a * 2 + b * 3

and hence

n + 1 = (a+1)*2+b*3

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Help proof by induction

**Physics Forums | Science Articles, Homework Help, Discussion**