AppliedNumeric answer

Four people must cross a bridge at night with one torch. At most two can cross at once, the torch must accompany every crossing, and a pair moves at the slower person’s pace. They take $1$ , $2$ , $5$ and $10$ minutes. What is the shortest total time?

Answer with a number. Fractions, powers and expressions like 23/6 or C(52,5) are read correctly in practice.

The worked solution is in Premium

The answer, the full working and the one idea to take away – for this and all 1,322 questions in the bank. Answer it in practice and your working is marked, with a known mistake named when you make one.

Start the 7-day free trial Practise it with Premium

Learn the method

Measuring and timing puzzles

Reported in interviews at

Optiver, IMC Trading

More games, decision theory and puzzles questions

What is the angle, in degrees, between the hour and minute hands of a clock at 3:15?Foundation
You have two eggs and a 100-storey building.Applied
A hundred closed doors.Applied
One of 1000 bottles of wine is poisoned, and the poison kills within a day.Applied
A balance, and coins of which exactly one is counterfeit and either heavy or light.Advanced
Five pirates in strict seniority split one hundred coins.Advanced

Four people must cross a bridge at night with one torch. · QuantMax

Four people must cross a bridge at night with one torch. At most two can cross at once, the torch must accompany every crossing, and a pair moves at the slower person’s pace. They take 111, 222, 555 and 101010 minutes. What is the shortest total time?

More games, decision theory and puzzles questions

Four people must cross a bridge at night with one torch. At most two can cross at once, the torch must accompany every crossing, and a pair moves at the slower person’s pace. They take $1$ , $2$ , $5$ and $10$ minutes. What is the shortest total time?