Respuesta :

iisAzrael
There are 10mm in 1cm
Therefore, 3.1cm

We are given

The books thickness is 31 millimeters

we know that

1 millimeters=0.1 centimeters

so, we can write

31 millimeters=31*1 millimeters

so, we can 1 millimeters

we get

31 millimeters=31*0.1 centimeters

now, we can multiply

we get

31 millimeters=3.1 centimeters..........Answer