Question 1203368
<pre>
v, amount of Irene's money before she buys.

PRICE       BOUGHT         COST
             10            (2/5)v
             24+10        18+(2/5)v
</pre>
The price of the two buys must be the same.

{{{(2/5)v/10=((2/5)v+18)/34}}}

{{{v/25=((2/5)v+18)/34}}}

{{{34v=25((2/5)v+18)}}}

{{{34v=10v+450}}}

{{{24v=450}}}

{{{highlight_green(v=18.75)}}}---------Irene's initial amount of money


1-pen price, {{{(2/5)(18.75)/10=(1/25)(18.75)=highlight_green(0.75)}}}


Cost for 10 pens was {{{0.75*10=7.5*dollars}}}.
She still had  {{{18.75-7.5=highlight(11.25)}}}   dollars after buying the first ten pens.