Need to purchase new TI -81 Calculator

The first graphing calculator was invented by Casio Computers. of Japan in 1985 It was the Casio FX-7000.The lead engineer on the Casio 7000 development team was Hideshi Fukaya. About 5 years later, Texas Instruments introduced its first .
The Ti 84 Plus was introduced in 2004. Before the TI 84 plus there werer other graphing calculators by TI: 80/81/82/83/85/86/92/73

Turn the calculator on. Press and release the 2ND key. Press and hold the up-arrow key to darken the screen/increase the contrast.

Obviously, to go the other way you use the down-arrow key instead of the up-arrow.

TI calculators have an annoying habit of dimming the screen when the batteries are changed so that it appears as if the calculator isn't turning on at all. Turn the calculator on (or at least press the ON key). Press and release the 2ND key. Press and hold the Up-arrow key for a few seconds and see whether the screen becomes legible.

Unfortunately the TI-81, unlike later models, does not have this capability built-in. You'll have to find and load a program to do this.

As far as I know, the TI-81 doesn't have a degree-minute-second entry mode the later TIs have. But to answer your question, you can always do it as:
 35 + 20 / 60
followed by ENTER if needed.

If you're in Radian mode instead of Degree mode, you'd have to follow up with MATH 6 to specify degrees instead of radians.

TI calculators have an annoying habit of dimming the screen when the batteries are changed so that it appears as if the calculator isn't turning on. Turn the calculator on (or at least press the ON key). Press and release the 2ND key. Press and hold the Up-arrow key for a few seconds and see whether the screen becomes legible.

try adjusting the contrast up using 2nd + up
just keep pressing it and it should turn back

Use the ^ key just above the divide. For example, 5 ^ 4 ENTER should give you 625.

I have the answer! GET A NEW CALCULATER...a calculator i don't think should last 8 years if u use it often...

You must use decimals. Like 1/2 = .5 3/4 = .75