Rounding to the Nearest Reciprocal (HP Prime, TI-84 Plus CE, Casio fx-CG 50)

Rounding to the Nearest Reciprocal   (HP Prime, TI-84 Plus CE, Casio fx-CG 50)

Introduction

The program ROUNDRCP rounds a number to the nearest 1/n. This function can come in handy in several applications, for example, when working with construction or measuring, when have to round results to the nearest eighth (1/8), inch (1/12) or sixteenth (1/16).

Presented here are versions for the HP Prime, TI-84 Plus CE, and Casio fx-CG 50.

HP Prime:  ROUNDRCP

EXPORT ROUNDRCP(a,n)

BEGIN

// Round a to the nearest 1/n

// 2017-11-21 EWS

LOCAL w;

w:=FP(ABS(a))*n;

w:=ROUND(w,0);

RETURN IP(a)+SIGN(a)*(w/n);

END;

The TI-84 Plus CE and Casio fx-CG 50 versions store the answer in X.

TI-84 Plus CE ROUNDRCP

"EWS 2017-11-21"

Input "NUMBER:",A

Input "TO 1/NTH:",N

fPart(abs(A))*N→W

round(W,0)→W

If A<0

Then

iPart(A)-(W/N)→X

Else

iPart(A)+(W/N)→X

End

Disp "X:",X

Casio fx-CG 50 ROUNDRCP

“NUMBER”?→A

“TO 1÷NTH”?→N

Frac ((Abs A))*N→N

RndFix(W,0)→W

If A<0

Then

Int (A)-(W÷N)→X

Else

Int(A)+(W÷N)→X

IfEnd

“X:”

X

Examples

Round π to the nearest 1/4:

ROUNDRCP(π, 4):  3.25 = 13/4

Round e^2 to the nearest 1/100:

ROUNDRCP(e^2, 100): 7.39 = 739/100

Round 1/4 + 2/7 + 3 1/3 to the nearest 1/16:

ROUNDRCP(1/4 + 2/7 + 3 + 1/3, 16):  3.875 = 31/8
(thank you to Joe Horn for pointing out my error, it's correct now.)

Tips 

If you do not have the sign (signum) function, you can compensate by the following code:

If X<0

Then

Return -1  (subtract operation)

Else

Return 1 (addition operation)

End

If your calculator does not have the Round to any number of decimal points function, such as the Casio fx-5800p or fx-3650p, you can manipulate the modes and use the Rnd function and a switch of modes, like this code:

Fix 0

X  (put number to round in display)

Rnd

Float/Norm (1/2)

Eddie

This blog is property of Edward Shore, 2017