Answer: 39 tins of cat food.
Explanation:
I am assuming the question is how the number of tins that can be bought.
Step 1 - Discounted price
With the discount a tin would cost;
= 80 * ( 1 - 25%)
= 60 cents
Step 2 - Packs of 6 purchased at discounted price
Every pack of 6 attracts 60 cents off which means that they are paying the price of 5 tins for 6 tins.
Price of 5 tins;
= 60 * 5
= $3
Out of $20, the number of packs of 6 he can buy are;
= 20/ 3
= 6.67
= 6 packs of 6
Step 3 - Number tins not in pack of 6 bought
If he buys 6 packs of 6 the amount of money left is;
= 20 - ( 6 * 3)
= $2
With these $2, he could buy;
= 200 cents/60 cents
= 3.333
= 3 tins
Step 4 - Total number of Tins bought
The total number of tins he can buy are therefore;
= 6 packs of 6 + 3 tins
= (6 * 6) + 3
= 39 tins of cat food.