Question: It is known that **ethyl** has a *stronger* inductive effect than **methyl**.
Its positive inductive effect is greater than methyl.

Then why does ethylamine has a $\mathrm{p}K\_\mathrm{b}$ of $3.35$ and methylamine has the $\mathrm{p}K\_\mathrm{b}$ of $3.34$
($\mathrm{p}K\_\mathrm{b}$ values in water)
Shouldn't the $\mathrm{p}K\_\mathrm{b}$ of ethylamine be **lower** than methylamine?

Answer: 
Ethylamine has a pKb slightly greater than that of methylamine.

As you are saying

> 
> It is known that ethyl is better than methyl for inductive effect. It's positive inductive effect is greater than methyl.
> 
> 
> 

is absolutely true. But the basicity in aqueous medium is not only determined by +I effect but also solvation of substituted ammonium cation.

Even though +I effect in ethylamine is more than that in methylamine, ethylamine is more bulkier and sterically hinders the formation of intermolecular H−bonds with water.

[![enter image description here](https://i.stack.imgur.com/vjSNl.gif)](https://i.stack.imgur.com/vjSNl.gif)
The difference of methyl’s and ethyl’s inductive effects is very small.

Likewise, the difference in $\mathrm{p}K\_\mathrm{b}$ values is very small.

Both are in the magnitude of *practically identical* or *within experimenal error.* As such, be happy that the theory holds true up to the point that the values are similar and don’t expect it to explain every last digit behind the decimal dot.