double then half

 in class, we learned a new strategy called doubling and halving

when you do this strategy you look to see how you can make it easier 

 5  x 48=240     I can half the 48 and it will become 24  then double the 5 to make it 10 which simplifies it to 10 x 24=240      10x24=240

6 x 3.5=21      I can half  the 6 to 3 then double the 3.5 to 7 which simplifies it to 3x7=21

3 x 7=21