Simple,
you have [tex]1 \frac{1}{3} [/tex]
to change any mixed number into an improper fraction,
you would take the whole number, multiply it by the denominator, add the
numerator to it, then put the original denominator from the mixed fraction
on the new numerator you have.
EXAMPLE:
[tex]1 \frac{1}{3}
(whole number*denominator)
1*3=3
(add numerator)
3+1=4
(use denominator from original)
[/tex]
Thus, making your answer,
[tex] \frac{4}{3} [/tex]
