Why it happens: this is the same trick as "23 hundreds = 2300". Break the numerator into the largest possible groups of 100 (or 10), turn each group into a whole, and let the leftover stay as the fractional part.
Tip: a quick shortcut — dividing by 100 moves every digit two places to the right, so 234 becomes 2.34.
Q2.
How many cm is 1 mm?
Answer
1 cm = 10 mm So 1 mm = 1⁄10 cm = 0.1 cm
Why it happens: if 10 equal millimetres fill one centimetre, then each millimetre must be one-tenth of a centimetre. The millimetre marks on your ruler are the tenth-marks of this chapter.
Q3.
How many cm is (a) 5 mm? (b) 12 mm?
Answer
(a) 5 mm = 5⁄10 cm = 0.5 cm
(b) 12 mm = 10 mm + 2 mm = 1 cm + 2⁄10 cm = 1.2 cm
Why it happens: once 10 mm are collected they make a whole centimetre, so 12 mm is 1 whole centimetre with 2 tenths left over.
Tip: to change mm into cm, just divide by 10 — that is, shift the decimal point one place to the left.
Q4.
How many mm is 5.6 cm?
Answer
5.6 cm = 5 cm + 0.6 cm 5 cm = 5 × 10 = 50 mm 0.6 cm = 6⁄10 cm = 6 mm Total = 50 + 6 = 56 mm
Why it happens: going from cm to mm we multiply by 10, which shifts the decimal point one place to the right: 5.6 → 56.