4th grade
posted by dk .
without multiplying, how do you know that the product of 399 and 48 is smaller than 20,722?

what is 50x400?

20,000

Since 399 is less than 400 and 48 is less than 50, then obviously the answer must be less than 20,000. Right?

the world in the 1400s

how can you show without multiplying that 4/9 is greater then 0.4