Question 770473
<pre>
{{{2/5}}}{{{""*""}}}{{{15/21}}}{{{""*""}}}{{{7/10}}}{{{""*""}}}{{{3/8}}}

Factor all numbers into primes:

{{{2/5}}}{{{""*""}}}{{{3*5/(3*7)}}}{{{""*""}}}{{{7/(2*5)}}}{{{""*""}}}{{{3/(2*2*2)}}}

Cancel a pair of 2's

{{{cross(2)/5}}}{{{""*""}}}{{{3*5/(3*7)}}}{{{""*""}}}{{{7/(cross(2)*5)}}}{{{""*""}}}{{{3/(2*2*2)}}}


{{{1/5}}}{{{""*""}}}{{{3*5/(3*7)}}}{{{""*""}}}{{{7/5}}}{{{""*""}}}{{{3/(2*2*2)}}}

Cancel a pair of 3's

{{{1/5}}}{{{""*""}}}{{{cross(3)*5/(cross(3)*7)}}}{{{""*""}}}{{{7/5}}}{{{""*""}}}{{{3/(2*2*2)}}}

{{{1/5}}}{{{""*""}}}{{{5/7}}}{{{""*""}}}{{{7/5}}}{{{""*""}}}{{{3/(2*2*2)}}}

Cancel a pair of 5's

{{{1/cross(5)}}}{{{""*""}}}{{{cross(5)/7}}}{{{""*""}}}{{{7/5}}}{{{""*""}}}{{{3/(2*2*2)}}}

{{{1/1}}}{{{""*""}}}{{{1/7}}}{{{""*""}}}{{{7/5}}}{{{""*""}}}{{{3/(2*2*2)}}}

Cancel a pair of 7's

{{{1/1}}}{{{""*""}}}{{{1/cross(7)}}}{{{""*""}}}{{{cross(7)/(5)}}}{{{""*""}}}{{{3/(2*2*2)}}}

{{{1/1}}}{{{""*""}}}{{{1/1}}}{{{""*""}}}{{{1/5}}}{{{""*""}}}{{{3/(2*2*2)}}}

So that becomes:

{{{3/(5*2*2*2)}}}

{{{3/40}}}

The next whole number to that is 1

We subtract that from 1 to find out what we must 
add to {{{3/40}}} to get the next whole number, 1.

{{{1}}}{{{""-""}}}{{{3/40}}}

Write 1 as {{{40/40}}}

{{{40/40}}}{{{""-""}}}{{{3/40}}}

Answer: {{{37/40}}}

Edwin</pre>