Estimate in ranges: worst case, most likely case, best case for a task.

Compute expected case using the PERT formula:
expectedCase = (bestCase + 4 * mostLikelyCase + worstCase) / 6

The pessimistic version of the formula is
expectedCase = (bestCase + 3 * mostLikelyCase + 2 * worstCase) / 6

Related:

### References

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Use PERT, not a single number even for small-scale estimations, particularly in unknown area.