So it takes (10n)/125min = 2n/25min to return to the previous position.

Counting the retrogression of 1 minute, this process takes an extra1+2n/25min.

Its cost is (1+2/25)+(1+2 * 2/25)+... (1+2 * n/25) = n+n (n+1)/25.

Donald Duck normally needs10000/100 =100 seconds, Mickey Mouse needs 10000/ 125=80 seconds.

Therefore, if Donald wants to win, he must let Mickey spend 100-80=20 minutes, that is, he must let Mickey spend.

N+n(n+ 1)/25 is greater than 20.

n+n(n+ 1)/25 & gt； 20

= & gtn(n+26)>500

The value of n can be easily obtained by solving inequality equations, where n >；; 12.87

So: n must be at least equal to 13 times.

Considering that it is level 6, it can be calculated by substituting a similar number. For example, 10 = "10 * 36 = 360 feels small, and then use 15 =" 15 * 4 1 to try it. If it is too big, you can find 18.

N must be at least equal to 13 times.