Question

4. Prove or disprove the following statement: Given two numbers, increasing both numbers by 10% results in two numbers whose difference is the same as the difference of the two original numbers. Give a numerical example and explain.​

Answer 1

Explanation:

increase by 10% is the same as multiplying by 1.1.

so, we get the assumption that

x - y = 1.1x - 1.1y = 1.1(x - y)

for the case that x <> y, now we can divide both sides by (x - y) and get

1 = 1.1

and that is wrong in all cases.

so, it is disproven for all x <> y.

for x = y the statement is true, the difference is in both cases 0.

e.g.

100 and 200

the difference is 100

100+10% = 110

200+10% = 220

and the difference is 110 (different to the original 100).

but 100 and 100, sure, the difference is 0, and the difference between 110 and 110 is still 0.

adding a % to a number means the size of the added part depends on the size of the basic number. the same % of a larger number is larger than the same % of a smaller number. therefore, the distance grows.