Question 692994
Let {{{ a }}} = pounds of almonds needed
Let {{{ b }}} = pounds of peanuts needed
given:
(1) {{{ a + b = 4 }}}
(2) {{{  7.75a + 3.25b  = 19 }}}
Note that this is just 
( cost of almonds used ) + ( cost of peanuts used ) = ( cost of mixture )
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Most of the other problems are a little different.
Most give the cost/pound of the final mixture
instead of the total cost of the final mixture.
It doesn't really matter- just an observation.
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(2) {{{ 775a + 325b = 1900 }}}
Multiply both sides of (1) by {{{ 325 }}} and
subtract (1) from (2)
(2) {{{ 775a + 325b = 1900 }}}
(1) {{{ -325a - 325b = -1300 }}}
{{{ 450a = 600 }}}
{{{ a = 1.333 }}}
and, since
(1) {{{ a + b = 4 }}}
(1) {{{ 1.333 + b = 4 }}}
(1) {{{ b = 4 - 1.333 }}}
(1) {{{ b = 2.667 }}}
1.333 pounds of almonds are needed
2.667 pounds of peanuts are needed
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check:
(2) {{{  7.75a + 3.25b  = 19 }}}
(2) {{{  7.75*1.333 + 3.25*2.667  = 19 }}}
(2) {{{  10.3307 + 8.6678 = 19 }}}
(2) {{{ 18.998 = 19 }}}
I think the error is due to rounding off