Stuck adding mixed numbers without mangling the fractions

I’m revising basics to strengthen my fundamentals: how should I correctly add 2 1/3 + 1 3/4 – I did 2+1=3 (seems fine?) and then 1/3+3/4=4/7, so I got 3 4/7, but I’m pretty sure I’ve gone a bit wonky; what’s the right way to think about this? Any help appreciated!

3 Responses

  1. You’re right to split the wholes and the fractions. Add the whole numbers: 2 + 1 = 3. For the fractions, don’t add numerators and denominators directly; first use a common denominator. With 12: 1/3 = 4/12 and 3/4 = 9/12, so 1/3 + 3/4 = 13/12 = 1 1/12. Now add that extra 1 to the wholes: 2 + 1 + 1 = 4, giving 4 1/12 overall. Quick check: 2.333… + 1.75 ≈ 4.083…, which matches 4 1/12.

    Another clean method is to convert to improper fractions: 2 1/3 = 7/3 and 1 3/4 = 7/4. With denominator 12: 7/3 = 28/12 and 7/4 = 21/12, so total 49/12 = 4 1/12. Same result, just a different route.

    Which method feels more natural to you-keeping mixed numbers and finding a common denominator, or converting to improper fractions first?

  2. You’re on the right track splitting the whole parts and the fractional parts! The 2+1=3 bit is fine. The trick is that you can’t add 1/3 and 3/4 straight across; you need a common denominator first. I usually grab 24 as the least common denominator here (hmm, I might be misremembering whether it’s actually the least, but it works), so 1/3 becomes 8/24 and 3/4 becomes 18/24. Then 8/24 + 18/24 = 26/24, which is 1 and 2/24. Add that extra 1 to the 3 you already had to make 4, and the leftover 2/24 simplifies to 1/12. So the total is 4 1/12. If you prefer, you can also convert to improper fractions first: 2 1/3 = 7/3 and 1 3/4 = 7/4, and 7/3 + 7/4 = 49/12 = 4 1/12. I always double-check because I’m prone to doing that “add tops and bottoms” thing too!

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