A fraction turns into a decimal when you can make its denominator 10, 100 or 1000 — that is why 3/8 becomes 375/1000 = 0.375, and why 1/3 never becomes an exact decimal at all. Going back the other way, read the decimal aloud: 0.35 is thirty-five hundredths, so it is 35/100, which simplifies to 7/20. Unit conversion is the same skill wearing a uniform: 1 km = 1000 m, so changing kilometres to metres moves every digit 3 places, exactly like multiplying by 1000. Ask first whether the answer should be bigger or smaller — a smaller unit always needs a bigger number.
Worked example
Problem Express 3/8 as a decimal.
A fraction is a division in disguise: 3/8 means 3 ÷ 8.
The quick way is to make the denominator a power of ten. 8 × 125 = 1000, so multiply the numerator by the same number: 3 × 125 = 375.
375/1000 is 375 thousandths, which is 0.375.
Tip Learn the common ones by heart — 1/2 = 0.5, 1/4 = 0.25, 3/4 = 0.75, 1/5 = 0.2, 1/8 = 0.125. They come up in every paper.