If there is #14/15# of the pizza left; then #1/15# has been eaten.
At most #3# pieces each #3/10# of a pizza can be made from a whole pizza (with #1/10# left over).
The amount eaten (#1/15#) is less than the amount that would have been left over after removing #3# pieces (i.e. #1/15 < 1/10#).
So #3# pieces could still be made from the left-over pizza.
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Alternate version:
#14/15 " pizza" div #3/10# " pizza/slice"#
#color(white)("XXX")=14/15 xx 10/3 " slices"#
#color(white)("XXX")14/cancel(15)_3 xx (cancel(10)^2)/3" slices"#
#color(white)("XXX")=28/9 = 3 1/9" slices"#
...but since we are (presumably) only dealing with full slices:
#color(white)("XXX")3" slices"#
