To get from an odd figure number to the next biggest odd figure number, add 8 rods.

(eg. Figure 35 to Figure 37)

To get from an even figure number to the next biggest even figure number, add 8 rods also.

(Eg. Figure 4 to Figure 6)

We know number of rods used in figure 2 = 15

Each time we add 8 once, the figure number increases by 2. If we add twice , it increases by 4. Add thrice, figure number increases by 6, and so on.

So this increase is twice the number of times we add 8 rods.

From Figure 2 to Figure 30 :

30 - 2 = 28
Figure number increased by 28.


28 ÷ 2 = 14

8 was added 14 times.

So number of rods used in Figure 30
= 15 + (14 x 8)
= 15 + 112
= 127

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