Answer:
He needs to buy 6 and 3/4 more pints.
Step-by-step explanation:
In order to find this, we first need to find out how much he has used. To do this, add together the two fractions of the whole that he has used.
2/5 + 3/10
4/10 + 3/10 = 7/10
Since he has used 7/10 of it already, we can multiply that by the original amount to find how much is gone.
7/10 * 20 = 14
So with 14 pints having been used, we know there is 6 pints left. To find how many more he needs to buy, subtract 6 from the amount he needs for the next painting.
12 and 3/4 - 6 = 6 and 3/4
