Difficulty adding RAND generated numbers

[Guest]

Having difficulty adding rand generated numbers, trying to create practice
worksheets for students using basic operations and integers.
A1: can be interchangable with +,-,x,or/
B2 C2 are the upper limits of numbers
B3 C3 the lower limits
B4...B23 is a rand() using B2 and B3 as limits; formula =RAND()*(B$2-B$3)+B$3
C4...C23 is a rand() using C2 and C3 as limits; formula =RAND()*(C$2-C$3)+C$3

Problem arises HERE when trying to create solution sheet:
=SUMPRODUCT(($A$1="+")*($B4+$C4)+($A$1="-")*($B4-$C4)+($A$1="X")*($B4*$C4)+IF($B4<>"",($A$1="/")*($B4/$C4),0))
Solutions are frequently off, e.q. generated numbers "5+19" solution sheet
says "25" is it something with the way the numbers are generated?
Perplexed!

 

[Guest]

RAND() is volatile; it recalculates every time the spreadsheet is
recalculated. Perhaps that is screwing up your calculations. Why not
generate a list of random numbers, copy them, paste them as values, and then
run your other formulas off those values?

Dave

 

[Guest]

Your formulas in B4 and C4 generaterandom numbers that may not be integers so
when you see 5 + 19 the underlying values might be 5.8 and 19.9 so when
added, this will show 25 if your result is formatted to show whole numbers
only.

To generate random integers change to

=INT(RAND()*(B$2-B$3+1)+B$3)

or, using RANDBETWEEN from Analysis ToolPak add-in

=RANDBETWEEN(B$2,B$3)

Additionally.....are you really using SUMPRODUCT as quoted? I wouldn't think
that's the most appropriate or efficient formula, perhaps try

=CHOOSE(MATCH($A$1,{"+","-","x","/"},0),B4+C4,B4-C4,B4*C4,B4/C4)