Your neighbor Steve needs your help 🌱
Utah's water shortage means Steve's family is redesigning their backyard — less lawn, more play areas, grow boxes, and drip irrigation. It's October 1st, and Steve is nervous: will the new yard be finished before winter?
You know something Steve doesn't: the Critical Path Method (CPM) — the project-management technique that tells you exactly how long a project will take and which tasks can't slip.
In this challenge you will…
Step 1 · Read the node
In the Critical Path Method, every task is drawn as a small table called a node. Each of the seven boxes has a job. Study the labeled node and the definitions below — you'll need them from memory in a moment.
- Early Start (ES) — the soonest a task can start.
- Early Finish (EF) — the soonest a task can be completed.
- Duration — the length of time it will take to complete the task.
- Late Start (LS) — the latest a task can start without impacting the schedule.
- Late Finish (LF) — the latest a task can be completed without impacting the schedule.
- Float — the flexibility to slip a task without impacting the schedule.
Now rebuild it from memory
Tap a label, then tap the box where it belongs.
Step 2 · The three-step method
The Critical Path Method is three passes over the network. Build a node for every task, connect them in order, then apply the formulas:
Watch it work
Step through this seven-task project. Watch where each number comes from — especially where paths split and rejoin.
Step 3 · Practice run: the vendor-selection project
This is the requirements-and-vendor project from your reading. Nine tasks, six possible paths from Start to Finish. Work the three passes one at a time — type a number and press Enter (or tap away) to check it. Wrong answers won't cost you anything; they'll earn you a hint.
Final challenge · The Water Wise backyard
After the most recent summer, Utah is still grappling with a serious water shortage — and your next-door neighbor Steve James feels it. His family's backyard is the heart of their gatherings, and the prospect of reduced irrigation water has them worried.
Steve and his wife decided to act: replace part of the lawn with features that need less water — play areas, a trampoline, grow boxes, and flower boxes. With a special family event less than six months away, Steve wants the new yard installed before winter so everything is in place and growing come spring. It is now October 1st, and Steve is nervous about getting it all done.
Together you sketched the Key Deliverables Network Diagram below. Now do what you've trained for: run the three passes, find the critical path, and tell Steve how long his project will take.
Key Deliverables Network Diagram (durations in days)
🎉 You did it — Steve can breathe easy!
Starting October 1st, the backyard wraps up around December 15 — before winter, with the whole yard ready to grow in spring. The tasks you highlighted in red are the ones Steve must watch: if any of them slips a single day, his finish date slips with it.
- Which tasks could slip, and by how many days, without delaying the yard?
- If Steve could hire help to shorten exactly one task, which one should it be — and why must it be on the critical path?
- The trampoline takes 35 days to arrive and install. What happens to the critical path if Steve finds one that ships in 20?