Question

A geologist had two rocks on a scale that weighed 3.3 kilograms together. Rock A was 0.1 of the total weight. How much did rock A weigh?

Answer 1

Multiply 3.3 by .1
3.3*0.1=.33
Rock A weighs .33 kilograms

Answer 2

Rock A had a weight of 0.33Kg

Explanation:

Let X: the weight of rock A and Y: the weight of rock B. The information available suggests that:

X + Y = 3.3 [Eq. one]

X = 0.1 (X + Y) [Eq. two]

Considering equation 2, we have that X = 0.1X + 0.1Y, which produces:

0.9X = 0.1Y ------------> 9X = Y. Substituting this last result in equation 1, you have:

X + 9X = 3.3, that is,

10X = 3.3 --------> X = 3.3 / 10 = 0.33Kg. As Y = 9X, then, Y = 9 (0.33) = 2.97Kg