An engine makes 400 revolutions per minute. It will make [blank] [blank] in 12 minutes.

To solve this problem, we can set up a proportion.

400 revolutions/1 minute = x revolutions/12 minutes

To solve this proportion, we can use cross products, which is multiplying the numerator of one fraction by the denominator of the other and setting these two products equal to one another.

400*12 = 1 * x

Now, let's simplify.

4800 = x

Therefore, if an engine makes 400 revolutions per minute, it will make 4800 revolutions in 12 minutes.