Question

My brother is 5 years older than me. My sister is 3 years younger than me. How old was my brother when my sister was m years old?

Answer 1

hmmmm

b = brother

s = sister

a = my age

so your brother is 5 years older, b = a + 5.

and your sister is 3 years younger, s = a - 3.

that means your sister is

$\bf \begin{cases} b=a+5\implies b-5=\boxed{a}\\ s=a-3\\[-0.5em] \hrulefill\\ s=\boxed{b-5}-3\implies s=b-8 \end{cases} \\\\\\ \stackrel{\textit{if your sister is "m" years old, say s = m}}{m=b-8}\implies \blacktriangleright m+8=b \blacktriangleleft$