For a and b take the answer and do the opposite of what the symbol tells you to do to the other number. For instance to solve 3×_=12 you would go 12÷3=4. 4 would be your answer. For letter c think that since you are making the number bigger you have to be adding or multiplying so put those two in and see which one works. Another thing you could notice is that the decimal goes 1 place to the right and if you multiply anything by 10 the decimal move 1 place to the right.
We could multiply or divide to get these boxes, but these are about multiplying or dividing by a power of 10, which can be done by counting digits, adding zeros or moving decimal points around.
To get from 2.5 to 250 we have to move the decimal point two places to the the right, appending a needed zero to do so. Each digit the decimal point moves is a factor of ten. Moving to the right is multiplying by 10. Moving to the left is dividing by 10.
Here we moved the decimal point two places to the right, two factors of 10, so we multiplied by 100. Two times 100 is 200 so we see we're in the ballpark.
a. 100
For part B we're going from 3.2 to .0032. That's moving three decimal places to the left, prepending zeros as needed, so dividing by three factors of 10, aka 1000.
b. 1000
To go from 0.17 to 1.7 is one decimal place to the right, multiplication by 10. Hopefully we can understand something around 2 is 10 times bigger than something around 0.2.
Ok so we know he used over 700 because he was charged more than 40. Then we take the $8.10 and divide 0.45 into it. This then gives you 18 more minutes. Then add 18 to 700 and you get 718 min.
