Let's denote the credits as C, units as U, and bells as B.
The question stem gives us the info that 12C = 8U + 5B ... (1)
We need to find out - the smallest integer number of units that can be exchanged for an integer number of bells, with no change left over
This is nothing but the ratio of U:B
Statement 115 credits can be exchanged for 4 units and 25 bells, with no change left over.15C = 4U + 25B ... (2)
We can equate C from this equation with equation (1) and get the ratio of U and B.
Although not needed we can do it after multiplying equations (1) by 5 and (2) by 4.
We have, 40U + 25B = 16U + 100B
Or, 24U = 75B
Or, 8U = 25B
So, we can exchange 25 B for 8 U. Statement 1 is sufficient and we eliminate options B, C, and E.
Statement 225 bells can be exchanged for 8 units, with no change left overThis statement directly gives us the answer. So statement 2 is sufficient.
So the answer is D.