Question 689894

let's the younger of two siblings be {{{x}}} (the older of two siblings) and {{{y}}} (the younger of two siblings)


 if the {{{sum}}} of their ages is {{{18}}}, we have

{{{x+y=18}}}.........eq. 1


 and if the difference is {{{10}}}, we have

{{{x-y=10}}}.........eq. 2


solve the system:


{{{x+y=18}}}.........eq. 1

{{{x-y=10}}}.........eq. 2
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{{{x+y=18}}}.........eq. 1.....solve for {{{x}}}


so, the younger of two siblings is {{{4}}} years old


{{{x=18-y}}}..........eq. 1a..........plug it in eq. 2


{{{x-y=10}}}.........eq. 2

{{{18-y-y=10}}}

{{{18-2y=10}}}

{{{18-10=2y}}}

{{{8=2y}}}

{{{8/2=y}}}

{{{highlight(y=4)}}}

now go to eq. 1a and find {{{x}}}


{{{x=18-y}}}..........eq. 1a

{{{x=18-4}}}

{{{highlight(x=14)}}}

so, the younger of two siblings is {{{4}}} years old