Question

By what percent will the product of two numbers change, if the first number increases by 70%, while the second number decreases by 40%.

Answer 1

2%

Explanation:

Let x be the first number

It increases by 70 %

The new number is

m = x+ .70x

= 1.7x

Let y be the second number

It decreases by 40 %

The new number is

n =y - .40 y

= .6y

The product of the original numbers is xy

The product of the new number is

mn = (1.7x * .6y) = 1.02xy

The new number is larger than the old number so it is an increase.

Percent increase is new - original divided by original times 100%

Percent increase = (1.02 xy - xy)

----------------- * 100%

xy

= .02 xy

------- * 100 %

xy

= .02 * 100 %

= 2%