Samuel purchased 2 1/2 lb of nuts for $10.50.how much will 5 1/4 lb cost?

First we need to know price per lb. we can calculate that with the info provided. So 10.5/2.5=4.2
So $4.20 per lb.
Double check that work before calculating the rest of the problem: 2.5(4.2)=10.5
So if 1 lb cost $4.20 we can multiply 5 1/4 or in decimal form 5.25(4.2)=22.05
So the total cost for 5 1/4 lbs is $22.05