The age of the universe is thought to be about 14 billion years. Assuming two significant figures, write this in powers of ten in (a) years, (b) seconds.

Question

anonymous · Answer

$$1.4\times10^{10},4.4\times10^{17}$$

anonymous · Answer

to get the answer in seconds you need to make these steps. in one minute there are 60seconds. therefore in one hour, there are 60 seconds times 60minuites = 3600seconds. in 1 day there are 24hrs, thus 24 times 3600s = 86400 seconds. 
in onr year there are 365 days, 365 times 86400 = 31536000s . Now you know that the universe is 14 billion years old approximate. 14,000,000,000 times 31536000 = 441504000000000000 seconds . 
in terms of powers of then = $$4.42\times10^{15}$$

anonymous · Answer

it seems long and complicated, but that is because i wrote every single step so that you can understand.

anonymous · Answer

fantastic, thank you!

anonymous · Answer

but with two significant figures it would be 4.4x10^15... right?

anonymous · Answer

no, as long as i know, 2 significant figures start from just behin the decimal point.

anonymous · Answer

i checked on the internet, and yes you are right, 4.4x10^15   
the problem is that i`ve learnt it the other way, that significant figures start from behind the decimal point, so i cant imagine how many times i did it like that in exams ...!

anonymous · Answer

That's right. 4.42 is "to 2 decimal places"; 4.4 is "to 2 significant figures". Pesky exam questions have to be read carefully. Sneaky suckers are setters sometimes.

anonymous · Answer

I still don't get this