Question 825501
{{{x}}}= hundreds digit.
Since the tens digit is twice the hundreds digit,
{{{2x}}}= tens digit.
Since the units digit is one more than twice the tens digit,
{{{2(2x)+1=4x+1}}}= units digit.
The value of the original three digit number is
{{{100x+10(2x)+4x+1=100x+20x+4x+1=124x+1}}} .
If the hundreds digit and the unit digit are interchanged, the value of the new number formed is
{{{100(4x+1)+10(2x)+x=400x+100+20x+x=421x+100}}}
The new number is 21 more than four times the original number means
{{{421x+100=4(124x+1)+21}}}
{{{421x+100=496x+4+21}}}
{{{421x+100=496x+25}}}
{{{421x+100-25=496x}}}
{{{421x+75=496x}}}
{{{75=496x-421x}}}
{{{75=75x}}}
{{{75/75=x}}}
{{{highlight(x=1)}}}
So,
{{{2x=2*1=highlight(2)}}}= tens digit, and
{{{4x+1=4*1+1=4+1=highlight(5)}}}= units digit.
The original number is {{{highlight(125)}}}
Reversing the digits you get {{{521}}} , and
{{{4*125+21=500+21=521}}} .