We need to see the other points

let the number of
Total number of people : adults + children
Total money earned from adults :
Total money earned from children :
Therefore, total money = money earned from each Adult and children.
Now, let's plug the value of x from equation [1] into equation [2]
let's plug the value of y in equation [1]
Hence, we get :
Correct option is C
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No the product will be less than 9/10.
This can be easily seen if the fractions are converted into decimals.
The decimal form of the product of 7/8 and 9/10 is 0.867 while the decimal form of 9/10 is 0.9. Therefore, the product of 7/8 and 9/10 is not greater than 9/10
26 x 72 = 1872
40 + 420 + 12 = 472
1872 - 472 = 1400 (the answer)