How do you solve #9m+n=20# and #m-4n=31# using substitution?

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Answer 1 · 2018-05-09T04:59:35

#color(blue)(m = 15, n = -4#

#9m + n = 20, " Eqn (1)"#

#m - 4n = 31, " Eqn (2)"#

#m = 31 + 4n#

Substituting value of m in terms of n in Eqn 91),

#9 * (31 + 4n) + n = 20#

#279 + 36n + n = 20#

#37n = -259#

#color(blue)(n = -259/37 = -4#

Substituting value of n in Eqn (2),

#m - 4 * -4 = 31#

#color(blue)(m = 31 - 16 = 15#