The LCD of 2 fractions is 840, one fraction is 1/30 what is the lowest possible denominator...

The LCD of 2 fractions is 840, one fraction is 1/30 what is the lowest possible denominator of the other fraction?
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[@TeddyR_Official]

I got 28 mentally. Apparently it’s wrong. Math is hard, lol.

[@evierice2230]

Me too, lol!

[@richmilito5417]

Why isn't it 28?

[@discobear5752]

@@richmilito5417 840 is divisible by 8, so you need an 8 as a factor in one of the denominators. 8 is not a factor of the known denominator, 30, so it must be a factor in the unknown denominator. 28 isn't divisible by 8; it's divisible by 4, so if you multiply 28 by 2 you then get a denominator which is divisible by 8.

[@pmw3839]

@@richmilito5417. Because if it was 28, the LCD would be 420, not 840.

[@pmw3839]

@@marinecorpswarrior915. No, if you multiply the denominators together you get a common denominator, but not necessarily the lowest common denominator. The LCD of 30 and 28 is 420, not 840.

[@russelllomando8460]

good one, thanks

[@danieldennis9831]

1/30 is 28/840. The prime factors of 840 are 2,3,5 and 7. I believe the next prime number is 11. 11/28 has prime factors of 2,7, 330/840+28/840. But they can be simplified to 420. I didn't figure it out without looking.

[@johnspencer9217]

have read your comments ; what you are not understanding is that the LCD 840 can not be reduced any more. so the has to be another denominator that works with 840 as the lowest capeesh ..Yes you can divide 30 into 840 =28 but this not the right ANS because the LCD can be reduced to 420 so you need to find the miss fit number 30 is ok has a zero so 28 is the key X by 2 =56 so test it 840 / 56 =15 it works so the miss denominator is 56 😀

[@charlesdellanno3379]

Very good. Keep up the good work. Chuck Del

[@juergenilse3259]

The answer is simple:it is (840/30) multiplied by GCD(30, 840/30). 840/30=28. The GCD of 30 and 28 is 2, so the result is 28*2=56.

[@virgilioisidro1021]

Why is 28 wrong when you are looking for the LCD? 😮

[@pmw3839]

We are not looking for the LCD. We already know that it is 840. We are looking for a denominator that, together with the denominator of 30, will give the LCD: 840.

[@bobcornwell403]

Me buffaloed. I know 28 isn't the answer. And I have tried factoring.

[@michaelhooper2491]

1/840 is the LOWEST FRACTION!!!

[@mike-yp1uk]

Wow

[@frankcote8106]

28 works.