susheelh wrote:

If s and t are positive integers, st + s + t cannot be

A. 5

B. 6

C. 7

D. 8

E. 9

susheelh wrote:

hsbinfy wrote:

take cases for(s,t)

(1,2)-5

(1,3)-7

(2,2)-8

(1,4)-9

only left is B-6

Thanks for the reply! One question - How did you Pick the number? Was it trial and error, some logic or practice?

Thanks in advance!

susheelh , I'm not

hsbinfy , but I used exactly the same numbers.

Trial and error, with a bit of method.

I started with s = t = 2

That yields 8.

It's clear that s = t = 3 is too big (9 is the first term with those numbers, never mind adding).

s = t = 1? Too small. = 4

So, increase t:

s = 1, t = 2 ---> 5

Increase t again. Why? These end numbers are small, there is multiplication, and one factor of 1 keeps things small.

s = 1, t = 3 ----> 7

s = 1, t = 4 ----> 9

I have 8, 5, 7, and 9.

Answer by POE must be 6

Answer B

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