SOLUTION: Mina ran 100 metre in 9.9 seconds. There was a 10% improvement from her previous best time. What was her previous best time?

Question 7222: Mina ran 100 metre in 9.9 seconds. There was a 10% improvement from her previous best time. What was her previous best time?
Answer by AK(1) (Show Source): You can put this solution on YOUR website!
let the previous time be 'a' secs.
in fresh attempt mina has improved upon time by 10%. hence time taken now is .9a secs.
ten percent improvement in time means that now mina has taken less time to cover same distance and the difference of time is 10%. Hence if she had done earler any distance in say 100 secs; same distance she is doing now in (100 - 10) 90 secs and percentage wise 90 of 100 will be
90 devided by 100 =9/10 or .9
therefore .9a =9.9 secs or a=9.9 devided by .9
since the decimal point is after one digit only from the right side both on top and bottom of this division sum, therefore the decimal point will cancel, both up and down.

so we will have a=99 devided by 9 = 11secs is the answer.
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