Final answer:
To make one car in the United States, 25 million workers are needed, while 12.5 million workers are needed to make 1 ton of grain. In Japan, 25 million workers are needed to make one car, while 20 million workers are needed to make 1 ton of grain.
Step-by-step explanation:
To find the number of workers needed, we need to calculate the productivity of each country for making cars and grain. Firstly, in the United States, one worker can produce 4 cars or 8 tons of grain a year. So, to make one car, we divide the number of workers (100 million) by the number of cars produced by one worker (4), giving us 25 million workers needed. Similarly, to make 1 ton of grain, we divide the number of workers (100 million) by the number of tons of grain produced by one worker (8), giving us 12.5 million workers needed.
In Japan, one worker can produce 4 cars or 5 tons of grain a year. So, to make one car, we divide the number of workers (100 million) by the number of cars produced by one worker (4), giving us 25 million workers needed. And to make 1 ton of grain, we divide the number of workers (100 million) by the number of tons of grain produced by one worker (5), giving us 20 million workers needed.