Question 761968
Let {{{ u }}} = the units digit
Let {{{ t }}} = the tens digit
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The value of the number is {{{ 10t + u }}}
given:
(1) {{{ 7*( 10t + u ) = 4*( 10u + t ) }}}
(2) {{{ t + u = 3 }}}
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(1) {{{ 70t + 7u = 40u + 4t }}}
(1) {{{ 66t = 33u }}}
(1) {{{ 2t = u }}}
by substitution:
(2) {{{ t + 2t = 3 }}}
(2) {{{ 3t = 3 }}}
(2) {{{ t = 1 }}}
and
(2) {{{ t + u = 3 }}}
(2) {{{ 1 + u = 3 }}}
(2) {{{ u = 2 }}}
The number is 12
check:
(1) {{{ 7*( 10t + u ) = 4*( 10u + t ) }}}
(1) {{{ 7*( 10*1 + 2 ) = 4*( 10*2 + 1 ) }}}
(1) {{{ 7*12 = 4*21 }}}
(1) {{{ 84 = 84 }}}
OK