<PRE><B>Question 654850</B>
Let {{{ a }}} = calories / cup of sunflower seeds
Let {{{ b }}} = calories / cup of raisins
given:
(1) {{{ 2a + 3b = 2900 }}} calories
(2) {{{ b = a - 400 }}} calories/cup
-----------------
(2) {{{ a - b = 400 }}}
Multiply both sides of (2) by {{{ 3 }}} and
add (2) and (1)
(1) {{{ 2a + 3b = 2900 }}} 
(2) {{{ 3a - 3b = 1200
{{{ 5a = 4100 }}}
{{{ a = 820 }}}
and, since
(2) {{{ b = a - 400 }}}
(2) {{{ b = 820 - 400 }}}
(2) {{{ b = 420 }}}
820 = calories / cup of sunflower seeds
420 = calories / cup of raisins
check:
(1) {{{ 2*820 + 3*420 = 2900 }}} 
(1) {{{ 1640 + 1260 = 2900 }}}
(1) {{{ 2900 = 2900 }}}
OK
</PRE>