When a person went to travelling, she estimated the traveled

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When a person went to travelling, she estimated the traveled distance and the speed. Then, she calculated the actual time. Is the difference between estimated and actual time smaller than 10minutes?
1) The difference between the estimated and actual distance is within 50miles
2) The difference between the estimated and actual velocity is within 50miles/1minutes
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Source: — Data Sufficiency |

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by Max@Math Revolution » Sun Sep 11, 2016 5:24 pm
There are 6 variables (estimated: v1, t1, d1, actual; v2, t2, d2) in the original condition, and 2 equations (estimated: v1t1=d1, actual; v2t2=d2). Hence, the correct answer is E.

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by Humblejohny » Mon Sep 12, 2016 9:16 am
Hi Max,

why not just divide difference in distance by difference in speed? 50/50 we get 1 minute which is smaller than 10.

Also if we take test cases,

what if d1 = 500 miles, d2 = 550 miles
for v1= 100, v2=50 then t1= 5 min, t2 = 11 min. difference = 6
for v1= 100, v2=150, then t1= 3.3 min, t2 = 5 min. difference = 2.7

what if d1=500, d2=450 then
For v1 = 100, v2 = 50 --> t1 = 5, t2= 9 difference = 4
For v1 = 100, v2 = 150 --> t1 = 5, t2= 3 min difference = 2

So combining together, the time difference is smaller than 10. So both together is sufficient right?