q5

Since she spent no time doing two activities at once, the question stem lets us set up the equation

c+e+p = 240

where c = minutes in class, e = minutes using email, and p = minutes on phone.

Statement (1) gives us another equation... c = 0.90e. We can plug this into the original equation to get

0.90e + e + p = 240 = 1.9e + p

however, we still have two unknown values in this equation and cannot solve for p.

Statement (2) gives us the equation c = 0.6(e+p). Again, we could plug this into the original equation to get

0.6e+0.6p+e+p = 240 = 1.6e+1.6p

but we still have 2 unknown values and cannot solve for p.

(1) and (2) Combined give us two different equations for c. We can then set them equal to each other...

c = 0.90e = 0.6(e+p)
0.30e = 0.6p
0.50e = p

Now, we have p in terms of e. Statement(1) gave us c in terms of e. Combining these we can arrive at

c+e+p = 240
0.90e+e+0.50e = 240
2.4e=240
e=100

0.50(100) = p
p=50

c=0.90(100)
c=90