opss in st(2) there's a small nuance
though found in OG-12 it comes from old OGs till now
the question to find integer value of quantity for $0.15 priced stamps bought.
let $0.15 priced stamps' quantity be A and $0.29 priced ones' be B, then 0.15A+0.29B=Cost of stamps
and we need to find A?
st(1) implies Cost Joanna paid was 4.40 and we assume buying B number of $0.29 priced stamps - we must find the possible integer value of B, if any. For this we assign two binomials 0.29B+0.15A=4.40 and assess the values of A and B. If we succeed to find the unique values for A and B, then st(1) is Sufficient, otherwise Not.
start with B as prime
B=1 -> 29+15A=440 AND A=(440-29)/15 Not Integer(NI)
B=2 -> 58+15A=440 AND A=(440-58)/15 NI
...
we can use common sense as a number is divisible by 5 if it ends by 0 or 5, and (440-29B) will end in 5 or 0 only if B=5,10,15
B=5, 145+15A=440, A=295/15 NI
B=10, 290+15A=440, A=150/15 good choice
B=15, 435+15A=440, A=5/15 NI
hence we have one unique set when A=10 and B=10 and can answer the question, Sufficient.
check: 0.29*10+0.15*10=4.40
st(2) A=B and we need to know the Cost which is in st(1) only (15A+29B=440 OR 44A=440, A=10) therefore st(2) Alone is Not Sufficient
answer A
Last edited by
pemdas on Fri Dec 23, 2011 8:11 am, edited 2 times in total.
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