Add them up!
0.590 mm
0.127 mm
+0.300 mm
_______
1.17 mm
For a geometric progression
a, b, c, d
there is a common ratio r equal to:
r = b/a = c/b = d/c
Let the missing number be x
r = x/50 = 450 /x
x² = 22500
x = 150
Answer:
a the assumption is that after the 60% discount, the 20% will contribute to the old price, not the adjusted price
b this is incorrect because the 20% discount will be added on after the 60% discount has been used
c the 500 dollars would turn to 100 dollars
d 40
e it would be best to first apply the 60% coupon first over the 20% coupon