A bag contains only two types of coins: 10 cent coins or 1 dollar coin...
Steps 1 & 2: Understand Question and Draw Inferences
If the number of 10-cent coins are ‘x’ and the number of 1-dollar coins is ‘y’, then we are told that x is less than or equal to y. The question is: what is the value of x?
Also, note that since ‘x’ and ‘y’ are number of coins, they must be non-negative integers.
Step 3: Analyze Statement 1
The total money in the bag due to 10-cent coins = 10x cents
The total money in the bag due to 1-dollar coins = y dollars or 100y cents
Total money in the bag = Total money due to 10-cent coins + Total money due to 1-dollar coins
16.50 * 100 = 10x + 100y
1650 = 10x + 100y
165 = x + 10y
This equation can have several integral solutions such as
if x = 5, y = 16
if x = 15, y = 15
if x = 25, y = 14, and so on.
Since x is less than equal to y, only the first two solutions are possible. ‘x’, whose value has to be found, can be 5 or 15.
INSUFFICIENT.
Step 4: Analyze Statement 2
If five 10-cent coins are replaced with five 1-dollar coins then the number of 10-cent coins become x – 5 and the number of 1-dollar coins become y + 5.
Then, y+5 = 2/3 * (x+y)
3y + 15 = 2x + 2y
y = 2x -15 ------(1)
We have to remember that x and y can only take non-negative integral values and x≤y
Substituting y from equation (1) in the given inequality, we have
x≤2x−15x≥15
x can have any value greater than or equal to 15.
For example,
if x = 15, then y = 2(15) – 15 = 15
if x = 16, then y = 2(16) – 15 = 17
and so on.
INSUFFCIENT.
Step 5: Analyze both statements together (if needed)
According to the information provided in Statement 1, x = 5 or x = 15.
According to the information provided in Statement 2, x = 15 or x = 16 or x = 17 and so on.
The common solution from the two statements is that x = 15
SUFFICIENT.
(C) is the correct answer.