book Maths Puzzle Numerical Ability

translate to a system of equations and solve.

the sum of two numbers is 30. their difference is 40. find the numbers.

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book Other Question

I am studying logarithms. I would like to know why d=log(b/a)becomes:
10^d=b/a
I have studied the properties of logarithms but the logarithms of produ what is the ratio of the number of nickles in a quarter to the number of quarters in a dollar?(the possibilites are.....5/4, 5/25, 4/5, or none of these)