A question from advanced engineering mathematics 4th edition (K. A. Stroud) , page 985, number 11, says: Maximize $P = 5.3x + 3.6y + 2.0z$ Subject to
$2.1x + 4.3y + 1.5z \le 70$
$3.2x + 1.4y + 2.2z \le 60$
$1.6x + 6.2y + 3.1z \le 100$
Working only with the decimals by not changing them to fractions gives decimals that are cumbersome to work with (too many decimals after the decimal point) but changing the decimals to fractions and working with fractions (I use a Casio fx - 991MS calculator to convert my decimal answers to fractions) would at a point give decimals which I can't convert to fractions on my Casio fx - 991MS calculator.
The answer at the back of the book gives: Pmax = $11.568$ ($x = 29/22, y = 14/11, z = 0$) to 3sf