Don't Ditch the Boat

Providing students with a physical model of the problem, that is, a full 2 litre bottle of water, 1 kilogram of Plasticine or play dough, and a jar of 20 counters, will help them to work through the problem by identifying the important information.
For five sailors, 2 litres of water, 1 kilogram of survival slab, and 20 pills must last for 2 days.
Suggest that students consider each of the rations separately. A logical path to the solution might be:
Five people for 2 days requires 10 equal parts (tenths).

Some students may divide the ratios in half to get a daily amount and then divide this amount into fifths. Similar reasoning can be applied to the situation in question 4, where there are four people in the boat.
2000 mL ÷ 8 = 250 mL per person per day (water)
1000 g ÷ 8 = 125 g per person per day (survival slab)
20 ÷ 8 = 21/2 pills per person per day (vitamins)
Students who are not familiar with metric units are likely to use innovative ways to divide the amounts. For example, eighths of a 2 litre bottle can be found by:

Repeat the pouring with quarters of a bottle to get eighths.

Answers to Activity

1. 200 mL
2. 100 g
3. 2
4. 250 mL of water, 125 g of survival slab, and 2 pills each day or 2 pills one day and 3 pills the other day.