JDesai01 wrote:If s and t are positive integers such that s/t = 64.12, which of the following could be the remainder when s is divided by t?
(a) 2
(b) 4
(c) 8
(d) 20
(e) 45
Answer is E. The gmat explanation is not very practical. Please post advice on how best to solve. Thanks
Agreed- the explanation in the OG is pretty obscure.
When we divide s by t we can always write:
s/t = q + r/t
where q is the 'quotient', and r is the 'remainder', where 0 <= r < t (so 0 <= r/t < 1). That's essentially the definition of the remainder, so is quite important to understand- many remainder questions will be difficult to answer otherwise. If
s/t = 64.12 = 64 + 12/100
then 64 is the quotient, while the fractional part, 12/100, is equal to r/t (compare with the other equation above). This doesn't mean 12 is the remainder, however- that would only be true if t was equal to 100. Still, we can find what values r might take. Rewriting:
r/t = 12/100
r/t = 3/25
25r = 3t
and if r and t are integers, the primes that divide the right side of this equation must also divide the left- in particular r must be divisible by 3. Only one answer choice is divisible by 3- E, or 45- so it's the only possible value of r among the answer choices.
There are many other possible values for r- any multiple of 3 would have been a possible answer, in fact.
