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WALT: use the inverse to find missing numbers in multiplication sums.


As we have discussed previously in class, the inverse is the opposite which means the inverse of division is multiplication and the inverse of multiplication is division.  We can use the inverse to work our numbers missing from a calculation.


As we know, 6 x 3 = 18.  

From knowing this sum, we also know that:

3 x 6 = 18,

18 ÷ 3 = 6 and

18 ÷ 6 = 3

This uses the inverse to show different sums using the same numbers within a sum.


From knowing these related sums, we can try to use our knowledge to complete missing numbers in the middle of calculations.  For example, if we have a multiplication sum in which a number is missing, we can use division to solve it.


For example, if we look at the following sum:        4 x ? = 32,   we can use the inverse to find the question mark.

Although you can count in 4s until you get to 32, the best way to work it out is to move the sum around so that you do, 32 ÷ 4.  By doing this sum, you arrive at the answer 8, which is what the ? is.


Therefore, to ensure you work out the correct sum, take the answer (32) and divide it by the other number in your sum (4)


We can check this answer by replacing the ? with our answer (8) in our original sum to see if it works.


So, 4 x 8 = 32 is our sum, which we can confirm is correct by working out 4 x 8.


Today's task is to follow the link:  This shows 10 questions with missing numbers.  Please answer the questions but also write the division sum that you have done to answer the question.  At the bottom of that page, there are other sets of questions that you can try, using harder times tables.  You can try these but don't worry if you cannot answer them, although you will be able to work out what sum you need to do.  Only try the questions that have multiplication in their title.