Question 193820
Let {{{I}}} = Isaac's age now
Let {{{K}}} = Kylie's age now
Let {{{B}}} = Brian's age now
given:
(1) {{{I = K + 9}}}
{{{B - 3}}} = Brian's age 3 years ago
(2) {{{I = 4*(B - 3)}}}
(3) {{{B = I - 18}}}
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I have 3 equations and 3 unknowns,
so it is solvable
Substitute (2) in (3)
(3) {{{B = I - 18}}}
(3) {{{B = 4*(B - 3) - 18}}}
(3) {{{B = 4B - 12 - 18}}}
(3) {{{3B = 30}}}
{{{B = 10}}}
And from (2):
(2) {{{I = 4*(10 - 3)}}}
(2) {{{I = 4*7}}}
(2) {{{I = 28}}}
And from (1):
(1) {{{28 = K + 9}}}
(1) {{{K = 19}}}
Kylie is 19
check answer:
Is Isaac nine years older than Kylie? Yes
Is Brian eighteen years younger than Isaac? Yes
Is Isaac four times as old as Brian was three years ago? Yes