Rewrite 5 1/4 as an improper fraction:
Multiply the whole number by the denominator of the fraction then add the numerator of the fraction and put over the denominator:
5 x 4 = 20 + 1 = 21
5 1/4 = 21/4
Ow divide the total amount (21/4) by the amount in each bag (5/8)
21/4 / 5/8
When dividing by a fraction flip the second fraction over and then multiply straight across:
21/4 / 5/8 = 21/4 x 8/5 = (21 x 8) / (4 x5) = 168/20 = 8 8/20 = 8 2/5 bags
He can fill 8 full bags and 2/5 of a other bag