How many seconds have you been alive at age 40?

Question

Solve in your head. Roughly how many seconds has a 40-year-old been alive? Aim: under 30 seconds.

Accepted Answer

The clean anchor to memorize: a year is about 3.15 	imes 10^7 seconds. (Check: 365 	imes 24 	imes 3600 = 31{,}536{,}000 \approx 3.15 	imes 10^7. A nice mnemonic is that \pi 	imes 10^7 seconds is almost exactly one year.) Then just multiply: 40 	imes 3.15 	imes 10^7 = 1.26 	imes 10^9. \approx 1.26 	ext{ billion seconds.} Takeaway. Keep a few conversion constants ready-made: \approx 3.15 	imes 10^7 seconds per year, 86{,}400 seconds per day, \approx 8{,}760 hours per year. With the year-in-seconds constant memorized, any "seconds since / until" question is a single multiplication.

How many seconds have you been alive at age 40?

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