Răspuns
100 km.
Explicație pas cu pas:
Consideram drumul impartit in 10 parti ( pt ca in prima zi parcurge 3/10 din el) si notam a zecea parte (1/10)din drum cu p .
._._._._._._._._._._. drumul are 10 parti (10p)
I) Daca in prima zi parcurge 3/10 din drum( adica 3 p) raman 7 parti
._._._._._._._._._._. 10p-3p=7p
II) Daca in a doua zi parcurge 2/7 din rest ( adica 2p din cele 7p) raman 5 parti
._._._._._._._. 7p-2p=5p
III) Daca in a treia zi parcurge 3/5 din ultimul rest (adica 3p din cele 5p) raman 2 parti
._._._._._. 5p-3p=2p
IV) Daca in a patra zi parcurge utimul rest (adica 2p) acesta reprezinta 20km.
=> 2p=20km <=> p=20:2 => p=10km
Am aflat ca o zecime din drum este 10km => 10p=10·10km =100km.
