Let S be the total number of students in the class.
From the math session information:
One group has 4 students, and all other groups have 5 students each.
This means S=4+5kM for some integer kM ≥0.
(If kM =0, then S=4 and there's only one group.
If kM >0, there are kM +1 groups).
This can be written as S≡4(mod5).
Or S≡−1(mod5).
From the biology session information:
One group has 4 students, and all other groups have 6 students each.
This means S=4+6kB for some integer kB ≥0. (If kB =0, then S=4 and there's only one group.
If kB >0, there are kB +1 groups).
This can be written as S≡4(mod6).
Or S≡−2(mod6).
Now we need to find an S that satisfies both congruences:
S≡4(mod5)
S≡4(mod6)
Since S has the same remainder when divided by 5 and 6, S must be of the form LCM(5,6)⋅q+4.
LCM(5,6)=30.
So, S=30q+4 for some non-negative integer q.
Let's list possible values for S:
If q=0, S=4.
If q=1, S=34.
If q=2, S=64.
If q=3, S=94.
And so on.
Let's check if S=4 is valid for the group structures.
Math: If S=4, it's 1 group of 4. (kM =0). Valid.
Biology: If S=4, it's 1 group of 4. (kB = 0). Valid.
Now, let's consider the history session information:
The same students (S) are divided so that one group has fewer than 7 students and all other groups have 7 students each.
Let N7 be the number of groups with 7 students each, and R be the number of students in the remaining group.
So, S = 7*N7 +R, where 0≤R<7.
The problem states "one group has fewer than 7 students", which means R cannot be 0. So 1≤R<7.
Let's test the possible values of S:
If S=4:
4 = 7*N7 +R
Since R≥1, N7 must be 0.
Then R=4. This satisfies 1≤R<7.
So, for S=4: Number of groups of 7 (N7) = 0. Remaining students (R) = 4.
Now, let's look at the available options. The options for "Groups of 7" are 2, 4, 6, 8, 10.
Since N7 =0 is not among the options for "Groups of 7", S=4 is not the total number of students we are looking for.
If S=34:
34 = 7*N7 +R
We know 1≤R<7.
If N7 = 4, 7×4=28. R=34−28=6. This is a valid remainder (1≤6<7).
So, for S=34: Number of groups of 7 (N7) = 4. Remaining students (R) = 6.
Let's check if these values are in the options:
"Groups of 7": 4 (is in options)
"Remaining students": 6 (is in options)
This combination (Groups of 7 = 4, Remaining students = 6) is jointly consistent with the given information.
Let's check other values of S just to be thorough, but we've likely found our answer.
If S=64:
64 = 7*N7 +R
N7 =9, 7×9=63. R=64−63=1. This is a valid remainder (1≤1<7).
So, for S=64: Number of groups of 7 (N7) = 9. Remaining students (R) = 1.
Is N7 = 9 in the "Groups of 7" options? No.
If S=94:
94 = 7*N7 +R
N7 =13, 7×13=91. R=94−91=3. This is a valid remainder (1≤3<7).
So, for S=94: Number of groups of 7 (N7) = 13. Remaining students (R) = 3.
Is N7 =13 in the "Groups of 7" options? No.
The only S value from our list that produces a valid N7 and R pair present in the options is S=34.
Therefore, the number of groups that have 7 students each in the history session is 4, and the number of students in the remaining history group is 6.