A man usually walks from A to B. How many hours does he normally walk

If he travelled 20% faster than normal, he would arrive one hour too early.
If he travelled 20% slower than normal, he would arrive one hour too late.

let t be the time in hours normally walked

t - t* 20% = 0.8 t = t - 1 => 0.2 t = 1
t + t* 20% = 1.2 t = t + 1 => 0.2 t = 1

so both give t = 1/0.2 = 5

Distance = Rate * Time

Traveling 20% faster means traveling 1.2 times as fast (100% + 20% = 120%)
Traveling 20% slower means traveling .8 times as fast (100% - 20% = 80%)

Let t = time in hours...

t - 1 = 1 hour early
t + 1 = 1 hour late

1.2 (t - 1) = .8 (t + 1)
1.2t - 1.2 = .8t + .8

Multiply equation by 10 to get rid of decimals.

12t - 12 = 8t + 8
4t = 20
t = 5 hours

5 hours

20% of 5 hours = 1 hour. Thus, 20% faster would take 4 hours and 20% slower would take 6 hours.

5 Hours.

5 hours - 20% = 4 hours...one hour too early
5 hours + 20% = 6 hours...one hour too late

5 hours