Rounding swaps an exact number for a tidy nearby one that is easier to say and work with. To round a whole number to the nearest 10, find the two tens it sits between and ask which one it is closer to.

Take 47. It lives between 40 and 50. The midpoint is 45, and 47 is past it — closer to 50 — so 47 rounds up to 50.

Press play, then replay it: each time a new two-digit number appears between its two tens, and you watch it snap to the nearer one.

Look only at the ones digit to decide:

• ones of 0,1,2,3,4 → round down (keep the ten).
• ones of 5,6,7,8,9 → round up (next ten).

A 5 in the ones place is exactly halfway between the two tens. By convention we always round it up: 25 becomes 30, and 65 becomes 70.

The same idea scales up. To round to the nearest 100, find the two hundreds the number sits between and pick the closer one — 347 rounds to 300, while 380 rounds to 400. To round to the nearest 1000, do the same with thousands: 6500 is halfway, so it rounds up to 7000.

Khan Academy walks through rounding to the nearest ten here: