Mental division of two fractions? I've got a non-calc paper coming up, and when going through a test, this fraction came up: (8)/(-0.4) -= (8)/(((-2)/(5))) Going through the answers he says: 8/2=4 I then assume he did -(4*5) so: (8)/(((-2)/(5))) = -20 I can see what he's done, but I don't see what's happening mathematically? (a)/((b)/(c))-=(a)/(b)*c

Matonya

Matonya

Answered question

2022-08-10

Mental division of two fractions?
I've got a non-calc paper coming up, and when going through a test, this fraction came up:
8 0.4 8 ( 2 5 )
Going through the answers he says:
8 / 2 = 4
I then assume he did -(4*5) so:
8 ( 2 5 ) = 20
I can see what he's done, but I don't see what's happening mathematically?
a b c a b c

Answer & Explanation

Lisa Acevedo

Lisa Acevedo

Beginner2022-08-11Added 18 answers

What he is using is that a 1 b = a b. That way he could transform a division involving decimals into simple integer multiplication.
Moselq8

Moselq8

Beginner2022-08-12Added 4 answers

We have that
a b c d = a b ÷ c d = a b d c = a d b c 8 2 5 = 8 1 2 5 = 8 ( 5 ) 2 1 = 40 2 = 20
For, of course any real numbers such that b , c , d 0

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