Tom swam to the bottom of a swimming pool that was 9 feet deep and he touched the bottom. He swam back to the surface. How many feet did Tom swim?

18 feet

Reason: he swam 9 feet going down the pool, but he didn’t just stay under there, he swam back up to the surface.
Thus we can 9 (feet for swimming to the bottom) plus 9 ( feet for swimming to the top).
In mathematical term we can say this in two ways.
9 + 9 = 18
Or
9 x 2 = 18

the law of definite proportions states samples of a compound will always contain the same proportion of elements by mass. in other words, a given compound will always contain the same elements in the same proportions by mass.the law of multiple proportions states when two elements combine with each other to form more than one compound, then the weights of one element that combine with a fixed weight of the other are in a ratio of small whole numbers.