Question

Rosa has a goal of running a total of 100 miles this month. Each day that she ran, she ran 5 miles. Which expression could Rosa use to determine how many miles she has left to run after running for d days?
A. 100 - 5d
B. 5d + 100
C. 100/5d
D. 5d - 100

Please provide an explanation how you came up with the answer, thank you.

Answer 1

Answer:

  A.  100 - 5d

Step-by-step explanation:

When d=0, Rosa has 100 miles remaining. That fact eliminates choices C and D, which do not give the value 100 when d=0.

After Rosa runs 1 day, she has 95 miles remaining. That eliminates choice B, which tells you she has 105 miles remaining.

The only viable choice is A.

_____

You could write this expression yourself by realizing that Rosa starts with 100 miles remaining and decreases that amount by 5 each time the value of d increases by 1. That is, the expression 5d represents the number of miles Rosa runs in d days. This number is subtracted from her goal to give the remaining miles, so 100-5d is the number she has remaining of her goal.