Source: High school physics (Chinese)
Problem Sets:
Problem
Each dry cell has an EMF of $1.5 \ \text{V}$ and the maximum current it can safely supply is $0.05 \ \text{A}$.
Use $8$ cells arranged as $2$ parallel branches of $4$ series cells each.
Cells in series add EMFs but keep the same current limit; cells in parallel keep the EMF but add current capacities.
To reach $6 \ \text{V}$: connect $n = 6/1.5 = 4$ cells in series. Such a string still has a current limit of only $0.05 \ \text{A}$.
To reach $0.1 \ \text{A}$: put $m = 0.1/0.05 = 2$ such strings in parallel.
Total cells: $n \times m = 4 \times 2 = 8$. Arrangement: $2$ parallel branches, each consisting of $4$ cells in series.