In a class, if 3 students are absent, then the rest of the students can be divided equally into 7 groups and if 7 students are absent, then the rest of the students can be divided equally into 9 groups. How many students are present in the class?
- AOption (a)
115
- BOption (b)
140
- COption (c)
87
- DOption (d)
101
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Correct answer
115
Why this answer is correct
Let, the total number of students are x.
If 3 students are absent, then the rest of the students can be divided equally into 7 groups.
Equal parts are (x - 3)/7
If 7 students are absent, then the rest of the students can be divided equally into 9 groups.
Equal parts are (x - 7)/9
According to the question,
(x - 3)/7 = (x - 7)/9 + 4
⇒ (9x - 27 - 7x + 49)/ 63 = 4
⇒ 2x + 22 = 63 × 4
⇒ 2x = 252 - 22
⇒ 2x = 230
⇒ x = 115.
Hence, the correct answer is "115".
Alternate Method By option elimination:
Option (1): 115
If 3 students are absent, then the rest of the students can be divided equally into 7 groups.
Equal parts are (115 - 3)/7 =112 / 7 = 16
If 7 students are absent, then the rest of the students can be divided equally into 9 groups.
Equal parts are (115 - 7)/9 = 108 / 9 = 12
Therefore two conditions are satisfied.
Option (2): 140
If 3 students are absent, then the rest of the students can be divided equally into 7 groups.
Equal parts are (140 - 3)/7 =137 does not divide by 7.
Option (3): 87
If 3 students are absent, then the rest of the students can be divided equally into 7 groups.
Equal parts are (87 - 3)/7 = 84/7 = 12.
If 7 students are absent, then the rest of the students can be divided equally into 9 groups.
Equal parts are (87 - 7)/9 = 80 does not divide by 9.
Option (4): 101
If 3 students are absent, then the rest of the students can be divided equally into 7 groups.
Equal parts are (101 - 3)/7 = 98/7 = 14.
If 7 students are absent, then the rest of the students can be divided equally into 9 groups.
Equal parts are (101 - 7)/9 = 94 does not divide by 9.
Hence, the correct answer is "115".

























