Question

a lending library has a fixed charge for frist 3 days and an additional charge for each day there after and sarita paid Rs 27 for a book kept for 7 day while susy paid Rs 21 for the book kept for 5 days find the fixed price and the charge of each day extra

Answer 1

$let \: fixed \: rate \: be \: x \: \: and \: charge \: of \: each \: day \: be \: y \\ x + 7y = 27 \\ x + 5y = 21 \\ on \: sub \: both \: equation \\ 7y - 5y = 27 - 21 \\ 2y = 6 \\ y = 3 \\ \\ x + 7 \times 3 = 27 \\ x = 27 - 21 = 6 \\ fixed \: rat \: is \: rs \: 6 \: and \: charges \: per \: day \: is \: rs \: 3$