Question 203409
The ratio of domestic stamps to foreign stamps in John’s stamp collection is 3:1. 
If John sold thirty of his domestic stamps, the ratio of domestic stamps to foreign stamps would be 1:2. 
How many foreign stamps does John have in his collection?
:
"The ratio of domestic stamps to foreign stamps in John’s stamp collection is 3:1."
{{{d/f}}} = {{{3/1}}}
d = 3f
:
"If John sold thirty of his domestic stamps, the ratio of domestic stamps to foreign stamps would be 1:2."
:
{{{(d-30)/f}}} = {{{1/2}}}
f = 2(d-30)
f = 2d - 60
replace d with 3f
f = 2(3f) - 60
f = 6f - 60
60 = 6f - f
60 = 5f
f = {{{60/5}}}
f = 12 foreign stamps
;
:
Check solution
d = 3(12
d = 36 domestic stamps
:
Check in statement:
" John sold thirty of his domestic stamps, the ratio of domestic stamps to foreign stamps would be 1:2."
36 - 30 = 6 stamps
6/12 = 1/2