Decimals that have the same value are

Decimals that have the same value are equivalent decimals. Equivalent decimals are decimal numbers that have the same value (the same amount). In other words equivalent decimal numbers have the same value but different number of decimals. For example: 
0.5 and 0.50 are equivalent decimals.
0.5 and 0.500
0.05 and 0.0500

Maybe the answer is 20mm. all i really did was just multiply, which is obvious.