Answer :
the strategy is called expanding notation because you are expanding that problem into small equations :)
Jack was multiplying 5×216.
To multiply this he first expanded 216.216 can be expanded as 216=200+16.
Jack multiplication numbers are : 5x216=5X(200+16)
This is of the form ax(b+c)
We can use the distributive property to distribute.The distributive property lets us multiply a sum by multiplying each addend separately and then add the products. ax(b+c)=axb+axc.Jack used the distributive property to distribute 5.
5x216=5x(200+16)=5x200+5x16.
He then multiplied the two numbers to get 1000+80=1080.
