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5A primatologist observes a troop of 120 monkeys in a reserve. Over the course of a month, 15% of the monkeys migrate to a neighboring forest, and then 1/4 of the remaining monkeys are fitted with GPS trackers for behavioral study. How many monkeys remain untracked after these changes?
First, 15% of 120 monkeys migrate: 0.15 × 120 = 18 monkeys.
So, 120 – 18 = 102 monkeys remain.
Then, 1/4 of 102 are fitted with GPS trackers: 102 ÷ 4 = 25.5. Since only whole monkeys can be tracked, we assume 25 are fitted (rounding down as per context).
Thus, untracked monkeys = 102 – 25 = 77.
A retired engineer helps build a solar-powered exhibit at a science museum. The exhibit requires 120 solar panels. He already installed 30% of them, and a volunteer installed 1/3 of the remaining panels last week. How many panels still need to be installed?
First, 30% of 120 = 0.3 × 120 = 36 panels installed by the engineer.
Remaining: 120 – 36 = 84 panels.
The volunteer installed 1/3 of 84: 84 ÷ 3 = 28.
So, installed so far: 36 + 28 = 64.
