Transcript A geologist has 10 rocks of equal weight. If 6 rocks and a 10-ounce weight balance on a scale with 4

A geologist has 10 rocks of equal weight. If 6 rocks and a 10-ounce weight balance
on a scale with 4 rocks and a 22-ounce weight, what is the weight of one of these
rocks in ounces?
a. 4
b. 5
Difficulty:
Medium
c. 6
d. 7
e. 8
HINT
If r is the weight of one rock, then the weight of 6 rocks and a 10-ounce weight
can be written as 6r + 10, and the weight of 4 rocks and a 22-ounce weight can
be written as 4r + 22. Since the two sides balance, these weights are equal.
C: 6
Explanation
Let r equal the weight of each rock, in ounces. The weight on one side of the scale
is 6r + 10 ounces and the weight on the other side is 4r + 22 ounces. Since the two
weights balance, you can write the equation 6r + 10 = 4r + 22. Solving this
equation yields r = 6.