A record of transactions for the month of May was as follows:

$\backslash$table$[[$Purchases$,$Sales$],[$May $1,($balance$)400$@$$5\mathrm{.}20,$May $3,200$@$$7\mathrm{.}00],[4,1,300$@$$5\mathrm{.}10,6,1,000$@$7\mathrm{.}00$