Price / Cost = $3.50/pound
For 4.2 pounds, total cost will be $3.50 × 4.2 = $14.70 <Type in calculator>
Or, through mental sums,
Cost of 1/10 pound = $3.50 ÷ 10 = $0.35
4.2 pound = 1/10 pound × 42
Cost of 4.2 pounds = $0.35 × 42
= $0.35 × 10 × 4 + (2 × $0.35)
= $3.50 × 4 + ($0.70)
= $14 + $0.70
= $14.70
Hope this helps! :)
