Question 948058
something is wrong with this problem...are you sure there is {{{90}}} coins, or ${{{15.10}}}

if {{{n=122}}} and {{{d= 212}}}, then {{{d+n= 122+212=334}}} coins, and
 
${{{0.05*122=6.1}}}
${{{0.10*212=21.2}}}

so, ${{{6.10+21.20=27.30}}} which is much more then ${{{15.10}}}


but, when I try with ${{{5.10}}}, it works


total coins :

{{{ n+d= 90}}}........equation 1

total money: ${{{5.10}}}

{{{0.05n+0.10d=5.10}}}.....equation 2

from equation 1 we have: {{{n=90-d}}}

{{{0.05(90-d)+0.10d=5.10}}}.....equation 2....solve for {{{d}}}

{{{4.5-0.05d+0.10d=5.10}}}

{{{0.05d=5.10-4.5}}}

{{{0.05d=0.6}}}

{{{d=0.6/0.05}}}

{{{highlight(d=12)}}}

then 
{{{n=90-12}}}
{{{highlight(n=78)}}}

check:

{{{0.05*78+0.10*12=5.10}}}
{{{3.90+1.20=5.10}}}
{{{5.10=5.10}}}