Four people need to cross a dark river at night

Four people need to cross a dark river at night. * They have only one torch and the river is too risky to cross without the torch. * If all people cross simultaneously then torch light wont be sufficient. * Speed of each person of crossing the river is different.cross time for each person is 1 min, 2 minutes, 7 minutes and 10 minutes. What is the shortest time needed for all four of them to cross the river ?

AQuA-RAT — Algebra Question Answering with Rationales (Ling et al., DeepMind, 2017) · train #5599