Problem
Since 1 lb = 16 oz, change 53 lb 12 oz to ounces: 53 x 16 = 848, plus 12 gives 860 oz.
Using one unit (ounces) lets us compare all the guesses on the same scale.
3.MD.A.2Analyze The UnitsCaleb's weight of 53 lb 12 oz is the same amount as 860 oz.
The 53 pounds turn into 848 ounces, and adding the leftover 12 ounces makes 860 ounces.
Each pound is 16 ounces, so 53 pounds is 53 equal groups of 16 ounces, which is exactly 53 times 16.
The 53-pound part and the 12-ounce part are the two pieces of the one weight with nothing missing and nothing counted twice, so putting them back together gives the whole weight.
Sophia: 55 lb = 55 x 16 = 880 oz. Lucas: 52 lb 5 oz = 52 x 16 + 5 = 832 + 5 = 837 oz. Mia is already 860 oz.
Once every guess is in ounces, comparing is just subtraction.
3.MD.A.2Analyze The UnitsCompare to actual 860 oz: Sophia off by 20, Lucas off by 23, Mia off by 0. Smallest error belongs to Mia.
The best estimate is the one with the smallest gap from the true weight, and Mia matched it exactly.
3.MD.A.2Make A Systematic ListThis only needs Grade 3 measurement sense: change everything to ounces, then the smallest gap wins!