A class was tested on two subjects-Mathematics and Physics. 80% of the...
Step 1: Question statement and Inferences
We are given the performance of students in a class test that consists of two subjects: Physics and Mathematics. Let’s say the total number of students who appeared for the quiz be N. So, the Venn diagram for the given information can be drawn as under:
Let
P = Number of students who passed only in Physics
M = Number of students who passed only in Mathematics
Z = Number of students who passed neither in Physics nor in Mathematics.
Let us now analyze the pieces of given information, one by one.
First, we are told that 80% of the students passed in Mathematics. The point to note here is that the statement doesn’t say ‘ONLY Mathematics’. Therefore, this percentage term includes students who passed only in Mathematics as well as students who passed in both Mathematics and Physics.
Therefore, we can write the equation:
M+180=80 of N
Or, M=0.8N - 180 . . . (1)
We are also told that the number of students who passed in Mathematics was 120 more than the number of students who passed in Physics.
Again, we note that this statement doesn’t say ‘Only Mathematics’ or ‘Only Physics’. The number of students who passed in Physics will be equal to the number of students who passed only in Physics PLUS the number of students who passed in both subjects.
Thus, we can write the equation:
M + 180 = (P+180) + 120
Or, M = P + 120 . . . (2)
Finally, we are given that
Or, M = 7P . . . (3)
Step 2: Finding required values
Substituting the value of M from Equation 3 in Equation 2:
7P = P + 120
6P = 120
P = 20
From Equation 2:
M = 140
From Equation 1:
140 = 0.8N – 180
N = 400
Step 3: Calculating the final answer
Now, P + 180 + M + Z = N
Substituting the values of P, M and Z in this equation, we get:
20 + 180 + 140 + Z = 400
340 + Z = 400
Z = 60
So, the number of students who failed in both the subjects is 60
Answer: Option (C)