The number a is 70% less than the positive number b. The number c is 80% greater than a. The number c is how many times b?

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1) The number a is 70% less than the positive number b
70% less means 100% - 70% = 30%
30% is 0.3
a = 0.3b

2) The number c is 80% greater than a
80% less means 100% + 80% = 180%
180% is 1.8
c = 1.8a

We want c in terms of b. Substitute equation 1 into equation 2:
c = 1.8(0.3b)
c = 0.54b