Question 875536
Let {{{ u }}} = the units digit
Let {{{ t }}} = the tens digit
Let {{{ h }}} = the hundreds digit
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(1) {{{ t = 0 }}}
(2) {{{ h = 3u }}}
(3) {{{ ( 100h + 10t + u ) + ( 100u + 10t + h ) = 404 }}}
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Substitute (1) into (3)
(3) {{{ ( 100h + 0 + u ) + ( 100u + 0 + h ) = 404 }}}
(3) {{{ 100h + h + 100u + u = 404 }}}
(3) {{{ 101h + 101u = 404 }}}
Divide both sides by {{{ 101 }}}
(3) {{{ h + u = 4 }}}
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Substitute (2) into (3)
(3) {{{ 3u + u = 4 }}}
(3) {{{ 4u = 4 }}}
(3) {{{ u = 1 }}}
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And
(2) {{{ h = 3u }}}
(2) {{{ h = 3 }}}
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The number is 301 
check answer:
{{{ 103 + 301 = 404 }}}
OK