Question

(ntse exam question) In a hostel, there was sufficient food for 200 students for 31 days. After 27 days 120 students left
the hostel. For how many extra days will the rest of food last for remaining students:
(1) 8 days (2) 6 days
(3) 12 days (4) 10 days

Answer 1

answer is 6 
solution;-
given students =200
given days =31
200 multiply with 31=6200
after days=27
students left=120
therefore now multiply 200 with 27=5400
from 28th day the quantity of food is 800 bc when we subtract the 5400 from 6200 the answer is 800 and the quantity of students is 80.
when u divide the 80 with 800 your ans is 10 mean 
but your quantity of left days is 4 so u subtract the 4 from 10 then ur answer is 6.
i hope u understand and this is helpful.

Answer 2

Given,
Total Students = 200

Food for them = 31 days

So, Quantity of food = 200 *31 = 6200 man-days

Till 27 days, quantity consumed = 27 *200 = 5400 man-days

Rest Quantity = 6200 - 5400 = 800 man-days

Remaining students = 200 - 120 = 80

Let reamining food will suffient for X days.
Now,
5400 + 80X = 6200
80X = 800
X = 10 days.