Question 762331
Let us say that after x minutes, both plans cost the same.

After x min, my plan will cost {{{15 + 0.05*x}}}
After x min, my friend's plan costs {{{20 + 0.02*x}}}

Equating the 2,

{{{15 + 0.05*x = 20 + 0.02*x}}}

Simplifying

{{{0.03*x = 5}}} or {{{x = 166.67}}}

Rounding off to nearest minute, the two plans will cost the same after {{{highlight(167)}}} minutes.

:)