The price of salt goes up by 9 cents. The old price goes up by four-fifth of new prices. Find old and new price.

Answer 1

n = o + 9

o + (4/5) n = n
so

n - 9 + 4 n/5 = n

4 n /5 = 9

4 n = 45

n = 45/4

o = 45/4 - 36/4 = 9/4
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now check
n = o + 9 = 9/4+36/4 = 45/4 yes
o + (4/5) n = n
9/4 + (4/5)(45/4) = n ?
5*9/4 = n ?
45/4 = n yes