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Statistics

Fit a straight line to data

Find the least-squares line y = ax + b that best matches a set of points.

Open in Trident

A line of best fit is the straight line that sits as close as possible to all your points. The calculator works out its slope (a) and its y-intercept (b).

The example points are x = 1 to 5 and y = 2, 4, 5, 4, 5. The best-fit line is y = 0.6x + 2.2.

Classic Graphing 84

Start on the main screen: Press 2nd then mode (QUIT) to get back to the home screen. Pressing clear on a menu also backs out of it.

  1. Type x into L1 and y into L2.

    stat11enter2enter3enter4enter5enter▶2enter4enter5enter4enter5enter

  2. Open STAT, move to CALC and choose LinReg(ax+b).

    stat▶4

  3. Leave the lists as L1 and L2. Move down to Calculate and press enter.

    ▼▼▼▼enter

You should seeSlope a = 0.6, intercept b = 2.2. The r values tell you how well the line fits.

If r does not show, turn on diagnostics in the mode settings.

Classic Graphing 84 key reference

Classic Scientific 30

Start on the main screen: Press 2nd then mode (QUIT) to leave any menu or screen and return to the calculation screen.

  1. Type x into L1 and y into L2.

    data1enter2enter3enter4enter5enter▶▲▲▲▲▲2enter4enter5enter4enter5enter

  2. Open the STAT menu (2nd then data) and choose LinReg ax+b. Accept the lists with enter.

    2ndstatdata3enterenterenter

You should seey=ax+b 1:a=0.6 2:b=2.2

Classic Scientific 30 key reference

Natural Scientific 991

Start on the main screen: Press MENU, then 1 (Calculate) to return to the main calculation screen. AC clears the line you are on.

  1. Open Statistics and choose y=a+bx, then type the x column.

    MENU621=2=3=4=5=

  2. Move right, back up to the top of the table, and type the y column.

    ▶▲▲▲▲▲2=4=5=4=5=AC

  3. Press OPTN and choose Regression Calc.

    OPTN3

You should seey=a+bx a=2.2 b=0.6

This model writes the line as a + bx, so a is the intercept and b is the slope.

Natural Scientific 991 key reference

Natural Color Graphing

Start on the main screen: Press MENU then 1 to open Run-Matrix, the main calculation screen. Press EXIT to back out of a bar or screen, and SHIFT then EXIT (QUIT) to return to the app start.

  1. Type x into List 1 and y into List 2.

    MENU21EXE2EXE3EXE4EXE5EXE▲▲▲▲▲▶2EXE4EXE5EXE4EXE5EXE

  2. Choose CALC (F2), then REG (F3), then X (F1) and finally ax+b (F1).

    F2F3F1F1

You should seePress COPY (F1) to store the line in the graph list, or DRAW (F6) to plot it.

Natural Color Graphing key reference

RPN Scientific 15

Start on the main screen: There is no menu to leave. Press the back arrow to clear a number you are typing, or CLx (g then back arrow) to clear the X register.

  1. Clear the statistics memory first, so old data cannot sneak into the answer.

    fCLR ΣGSB

  2. For each pair, key in y, press ENTER, key in x, then press Σ+.

    2ENTER1Σ+4ENTER2Σ+5ENTER3Σ+4ENTER4Σ+5ENTER5Σ+

  3. Press f then Σ+ (L.R.). The intercept appears in X and the slope in Y.

    fL.R.Σ+

You should see0.6000 2.2000

RPN Scientific 15 key reference

RPN Advanced 42

Start on the main screen: Press EXIT (once or twice) to close any menu and return to the plain stack view of Y and X.

  1. For each pair, key in y, press ENTER, key in x, then press the Σ+ key.

    2ENTER1Σ+4ENTER2Σ+5ENTER3Σ+4ENTER4Σ+5ENTER5Σ+

  2. Open the STAT menu (shift, ÷) then FIT (the last menu key). The menu now offers FCX, FCY, SLP, YIN and r.

    ⇧STAT÷XEQ

  3. Press the third key for the slope (SLP).

    √x

You should seex: 0.6000

The fourth key (YIN) gives the intercept, 2.2000.

RPN Advanced 42 key reference

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