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# Z-Confidence Interval for mean and proportion for the HP-15C

This program is Copyright © 2002 by Raúl Lión Arrese and is used here by permission.

This program is supplied without representation or warranty of any kind. Raúl Lión Arrese and The Museum of HP Calculators therefore assume no responsibility and shall have no liability, consequential or otherwise, of any kind arising from the use of this program material or any part thereof.

## Overview

Confidence interval for mean and sample size
The first program let us know the conf. interval for a mean and error
mean ENTER desv ENTER n ENTER Zalfa/2 GSB 1 → interval limits in X and Y. Error in R0
Writing the new error and calling the second one, we'll get the new sample size
new error GSB 4 → new sample size

Lbls&regs: LBL1 and LBL4. Reg I, 0,1

### Example

Example: mean 15200, desv 2250, sample size 100, confidence level 99% (Zalfa/2= 2.576)
15200 ENTER 2250 ENTER 100 ENTER 2.576 GSB 1 → X: 14620.4 Y: 15779.6 RCL 0: 579.6
and then 500 GSB 4 → 134.3745

```LBL 1
STO I
X⇔Y
√x
÷
X⇔Y
STO × I
×
STO 0
+
X⇔Y
RCL - 0
RTN
LBL 4
RCL ÷ I
1/X
x2
RTN
```

## Overview

Confidence interval for proportion and sample size
They work exactly as the two of above but with different entry data:
proportion ENTER sample size ENTER Zalfa/2 GSB 2 → as above
new error GSB 5 → new sample size

Lbls&regs: LBL 2, LBL 5. Reg I, 0, 1

### Example

Example: proportion 0.75, sample size 120, confidence level 95% (Zalfa/2= 1.96)
0.75 ENTER 120 ENTER 1,96 GSB 2 → x: 0.6725 y: 08275 RCL 0: 0.0775
and then 0.05 GSB 5 → 288.12

```LBL 2
1
R↑
STO 1
-
LST X
×
STO I
R↑
÷
√x
X⇔Y
×
LST X
x2
STO × I
R↓
STO 0
RCL 1
RCL + 0
RCL 1
RCL - 0
RTN
LBL 5
x2
RCL ÷ I
1/X
RTN
```