Carcass wrote:
If m and p are positive integers and \(m^2 + p^2 < 100\), what is the greatest possible value of mp ?
A. 36
B. 42
C. 48
D. 49
E. 51
Let's
test some pairs of values.
Since m and p are POSITIVE INTEGERS, we won't have a ton of options
Try m = 9 and p = 4 (aside: if m = 9, then 4 is the biggest possible value of p)
In this case, mp = (9)(4) = 36
Try m = 8 and p = 5 (aside: if m = 8, then 5 is the biggest possible value of p)
In this case, mp = (8)(5) = 40
Try m = 7 and p = 7 (aside: if m = 7, then 7 is the biggest possible value of p)
In this case, mp = (7)(7) = 49
Try m = 6 and p = 7 (aside: if m = 6, then 7 is the biggest possible value of p)
In this case, mp = (6)(7) = 42
Try m = 5 and p = 8 At this point, we can see that, if we continue, we'll be duplicating the work we did earlier.
That is, this case (m = 5 and p = 8) is the SAME as the 2nd case we examined.
If we continue, the next case we test will be m = 4 and p = 9. which is the SAME as the 1st case we examined, etc.
Since we've now tested all possible (and relevant) cases, we can see that the maximum value of mp is 49
Answer: D