1:40 because if we think of this just like a fraction

that simplifys down to

and because fraction simplifications are similar (related to each other) we can concur that these would be too.
Enjoy!=)
A(b-c)=d solution is number 2. Attachment added
The total number of pencils is 2,160. When estimating to the nearest hundredth one gets 2,200, which is an underestimate.
The advantage of underestimating is that your answer is more accurate than an overestimate.
4/2 it goes over 4 and up 2