Quote by: suz855Q1. Given A+B=80

B+C=70

A+C=90

If we sum them altogether, we'll have 2 x (A+B+C) = 240, therefore, A+B+C = 120

Problem will then be solved, since A+B=80, therefore C = 40 & so on.....

Q2. Given the total mirrors were 36, therefore 1/4 of them will be 9 mirrors.

Since the mass of the box is constant, the 11.25kg will be the mass of the 9 mirrors, we can then find the mass of 1 mirror

(1mirror) --> 11.25 divide by 9 = 1.25kg

Given mass of 1 mirror is 5/7 the mass of the box, mass of box shall be 1.25 divided by 5 multiply by 7 which is 1.75kg.

Puting everything together 1.75kg + 36 x 1.25kg = 46.75kg

Q3. [ | ][ | ][ | ][ | ][ | ]

<-----------> <---->

files left

(left)--> 3u = 1200 books, therefore number of files equal to number of books which will be 400

Since given each file cost 2.50 more than a book, 400 files shall cost 400 x 2.50 = $1000 more

5u --> 1000, therefore, 1u = 200

cost of a book = 200 divide 400 = $0.5