hi I'm Ashley and welcome to dividing unknown numbers in this video we are
going to learn how to find the unknown in a division problem are you ready
let's go
like when multiplying with unknowns it is important to understand the concept
of fact families it's also important to understand this concept with dividing
unknown numbers so look at my list here I have 2 times 3 is 6 3 times 2 is 6
flip those around I have 6 divided by 3 equals 2 and Bicks divided by 2 equals 3
so these last two here are the ones we need to pay the most attention to at the
moment notice how my 3 and my two switch places this is what we will do to solve
for our unknown so for example if I have the number or the problem 15 divided by
an unknown equals 5 how would I solve for that unknown well I will write the
other problem in this fact family okay 15 divided by hmm remember I'm going to
switch the places 5 and the unknown so 15 divided by 5 is equal to the unknown
and if you know your facts 15 divided by 5 equals 3 so our unknown is 3 let's try
this with a couple problems from our game my first problem here is 18 divided
by an unknown equals 2 so we're going to use the other division problem in this
problems fact family to find our unknown so I will switch the unknown and the 2 I
now have 18 divided by 2 equals our unknown and do you know your facts 18
divided by 2 equals 9
let's try another one okay my next one here is 42 divided by an unknown equals
2 if I switch my unknown and my 2 around I have 42 divided by 2 equals my unknown
now this number here is a little bit bigger than the facts I have memorized
so I will divide this using the division house 42 divided by 2 okay so 2 goes
into 4 twice 2 times 2 is 4 let me subtract 0 I will
bring down my 2 2 goes into 2 one time and that is my final answer
21 now let's work this backwards so that we can make sure we have got our correct
answer I'm going to take our answer 21 times 2 and see if we get 42 so 21
times 2 2 times 1 is 2 and 2 times 2 is 4 42 so we know 42 divided by 21 equals
2 we were correct great job now go
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