Question 281170
Let {{{r}}} = pounds of raisins they should buy
Let {{{s}}} = pounds of sunflower seeds they should buy
given:
Cost of sunflower seeds = {{{400s}}} (in cents)
Cost of raisins = {{{150r}}} (in cents)
(1) {{{150r + 400s = 3400}}}
and
(2) {{{r = 3s}}}
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By substitution:
(1) {{{150*3s + 400s = 3400}}}
{{{450s + 400s = 3400}}}
{{{850s = 3400}}}
{{{s = 4}}}
and, since
{{{r = 3s}}}
{{{r = 12}}}
They should buy 12 pounds of raisins and 4 pounds of sunflower seeds
check:
(1) {{{150r + 400s = 3400}}}
(1) {{{150*12 + 400*4 = 3400}}}
{{{1800 + 1600 = 3400}}}
{{{3400 = 3400}}}
OK