Question 224788
We know that {{{(139 beats)/(60 seconds)}}} and {{{(162 beats)/(60 seconds)}}}.
So, our equation is for the 139 beats:
{{{(139 beats)/(60 seconds)=(X beats)/(10 seconds)}}}
We can cross multiply this:
{{{139*10=X*60}}}
So, simplify:
{{{1390=60X}}}
Divide by 60:
{{{X=23.167}}}
Same procedure for 162 beats:
{{{(162 beats)/(60 seconds)=(X beats)/(10 seconds)}}}
{{{162*10=X*60}}}
{{{1620=60X}}}
{{{27=X}}}

Now, if you are looking for whole beats that she needs to count, the answer would be between 24 and 27 beast in 10 seconds, since 23 beats would have her heart rate below 139, which is our minimum.
Since she can't count 23.167, this may be the answer they are looking for, but if you can use exact number then it's between 23.167 and 27...though even I would have a great deal of difficulty counting 23.167 beats.