Evaluate 390mm to 13cm as a ratio in its lowest term

First, change 13 cm to mm. Or you could change 390 mm to cm. What is that number?

first, change 13 cm to mm. Or you could change 390 mm to cm. What is that number?

What number you talking

Change mm to cm, or change cm to mm. Doesn't matter. You want mm and mm or cm and cm.

390 mm = x cm?

It is perhaps easier to convert the bigger unit into the small unit.

390 mm : 13 cm

Convert 13 cm into mm, recall that 1 cm is equivalent to 10 mm.
Then, replace 13 cm (by the number of mm that you just get) into the ratio.
Simplify by taking out common factors.

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