Question 1120155
.
<pre>
An equivalent re-phrasing is that you can group the stamps sold in sets containing (15 of 5-centavo + 6 of 6-centavo + 4 of 30-centavo) stamps.


Each group contains 15+6+4 = 25 stamps.


15000 stamps contain {{{15000/25}}} = 600 such groups, i.e. contain

    15*600 of 5-centavo

     6*600 of 6-centavo

     4*600 of 30-centavo  stamps.


Now the number under the question is  15*600 - 6*600 = 9*600 = 5400.
</pre>

<U>Answer</U>. The number under the question is  5400  stamps.