Question 126990
Cost of the compass is C.
Cost of the ruler is R.

C + R = 4

C = R + .9


So, (R + .9) + R = 4


2R + .9 = 4


2R = 4 - .9


2R = 3.1


R = 1.55


C = 1.55 + .9 = 2.45


Check:
1.55 + 2.45 = 4.00