How to change a fraction into a decimal

This is a partial solution for I do not have the TI89 titanium with me.
1. The easiest way is to insert the decimal mark (. dot or , comma) at the end of one of the elements of the fraction (numerator or denominator).

Ex: if you enter 1/2 the calculator displays the fraction 1/2, but if you enter 1./2 or 1/2. or 1./2. it displays 0.5

2. You can also configure the EXACT/APPROXIMATE mode option of the calculator ( Press Mode then scroll till you see exact/approximate) then choose AUTO, EXACT, or APPROXIMATE.

In the EXACT option the calculator will perform exact algebra ( Pi remains Pi not 3.14159... ).
In the APPROXIMATE option, calculations are performed numerically (everything is treated as a decimal number.)

In the AUTO option the calculator will try its best to keep the results as exact as possible :
x/6 + 1/2 yields x/6 + 1/2
x/6. + 1/2 becomes .166666..x +1/2
x/6. + 1./2 becomes .16666..x +0.5

My suggestion ( if you allow me) : Leave the calculator set on AUTO, and convert to decimals as needed by putting the decimal mark at the end of an integer.

I hope it helps.