18 x 100 = 1800
18 times 100 is 1800. If 18 feels awkward, take 20 x 100 = 2000 and subtract 2 x 100 = 200. The answer 1800 is also exactly thirty minutes measured in seconds.
18 × 100 = 1,800
Adding 18 to itself 100 times gives the same answer.
Round up, then take the extra off
18 sits just below 20, so the easiest route is to overshoot and correct. 20 x 100 = 2000, then subtract 2 x 100 = 200, which leaves 1800. The same overshoot works for any multiplier ending in 8 or 9, where counting up from the round number is faster than multiplying directly.
Why 1800 shows up in software
1800 seconds is exactly 30 minutes. Session timeouts, cache lifetimes and scheduled jobs are almost always written in seconds, so 1800 appears in configuration files far more often than 30 does.
Checks on the answer
The digits of 1800 add up to 9, so 1800 divides cleanly by 9: 9 x 200 = 1800. It also splits as 36 x 50 and 2 x 900. If a number you have written down fails the digit-sum test, the multiplication went wrong somewhere.
Nearby
- 17 x 100 = 1700
- 36 x 100 = 3600, double this answer and one hour in seconds