An overseas phone call is charged at one rate for the first minute and at a different rate for each additional minute. If a 7 minute call costs $10 and a 4 minute call costs $6.40, find each rate.
Let call charge for the first minute be $x, and each additional minute be $y.
By given conditions,
Subtract (ii) from (i), we have
Substitute y from (iii) in (ii),
Thus call rates are for first minute $2.80 and each additional minute $1.20 .