A student recently wrote us: "This question is really not fair without a calculator. C and D are so close that by using typical rounding rules such that 13/98 is approximately 10/100 the answer would be 100 mm which would lead you to believe that C is correct. How are we supposed to know 13/98 = 0.133 off the top of our heads?"
One should not round 13 to 10. A general rule of thumb is that one shouldn't round by much more than 10%, and rounding 13 to 10 is a 30% round. Rounding 98 to a 100 is a much safer round, and elementary division tells us that 13/100 is 0.133. Lastly, if one encounters a calculation where multiple numbers need to be rounded, keep track of when a number is rounded down or up. The number rounds up and down should be balanced to an accurate approximation of the correct answer.
Thanks for your question. I hope this helps!
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