Measuring Four Cups of Flour
Date: 27 Feb 1995 12:14:33 -0500 From: Kay Moore Subject: We need help! Dear Dr. Math, A third grade class at our school, Ayden Elementary, needs help with this problem. A cook is making a cake that requires four cups of flour. She only has two measures, which hold 7 cups and 10 cups. How can she use her measures to measure exactly 4 cups? We know you will try to help us. Thank you, Mrs. Moore's Fourth Grade Class
Date: 27 Feb 1995 16:29:13 -0500 From: Dr. Ken Subject: Re: We need help! Hello there! The key to doing this problem is that you have to be kind of tricky, and it helps if you've seen this kind of problem before. Anyway, here's the best thing I can think of: think about what amounts you can get by filling one cup up with flour, and then pouring all that will fit from there into the other cup. For instance, if you filled up the 10 cup measure with flour, and then poured all that will fit into the 7 cup measure, you'd have 3 cups left in the bigger measuring cup (because 10 - 7 = 3). So that's how you could get 3 cups. I'll let you explore this concept some to see how you might get 4 cups. Write back if you still can't figure it out! Here's another problem for you: A cook is making a cake, and she needs to use 3 cups of milk. However, she only has one measuring cup (what the heck kind of cook only has one measuring cup??? And for that matter, what the heck kind of cook only has a 7 cup measure and a 10 cup measure???), and that measuring cup is cylindrical and holds 6 cups. How can she measure 3 cups of milk using only her 6 cup measure? -Ken "Dr." Math
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