Writing to explain use rounding to estimate the product 12×9. then, use compensation to find the total cost for 12 books that were $9 each, would she get a good estimate? explain

So if we do not know what 12 times 9 is then we can round 9 to 10 and get
12 times 10
most people can multiply by ten so this should be easy so
12 times 10=120

12 times 9=108
she was off by 12 so a 10% deviation error

another way to do it is you multiply 12 by 10 and get 10 12's
then you subtract 1  12 and get 9  12's

The ratio of blue marbles to red marbles is 35:15. To test his hypothesis in the best way, he should make sure that the total number of marbles he draws is 100. In other words, both sides of the ratio added together should equal 100. Right now, both sides equal 50 (35 + 15 = 50). To get to 100, double both sides of the ratio. Now, the ratio is 70:30. Based on the 50 marbles Sam drew, there are 70 blue marbles and 30 red marbles, meaning Sam's hypothesis is incorrect, and there are more blue marbles than red.