So only 12 of the values are used.

[Rubik]

Why is m = 2 and n = 3.. I am trying to solve a similar pool question yet I am not sure how to get m and n as in this solution they are given n and m but how do I work it out for myself?

A 20-ft-by-30-ft swimming pool is filled with water. The depth is measured at 5-ft intervals, starting at one corner of the pool, and the values are recorded in the table. Estimate the volume of water using the Midpoint Rule with m = 2 and n = 3.
Table given:
___0 __5__10___15__20__25___30
0__2__ 3__ 4___ 6___7___8____8
5__2__ 3__ 4___ 6__ 8___10___ 8
10_2__4__ 6___ 8___10__12__10
15_2__3__ 4___ 5___6___7___ 7
20_2__2__ 2___ 2___3___4___ 4

 

[lurflurf]

By counting. In this method one uses the odd values. We have a 7 by 5 array
m=(7-1)/2=3
n=(5-1)/2=2

The # are the values to include and * those not to.

___0 __5__10___15__20__25___30
0__*__ *__ *___ *___*___*____*
5__*__ #__ *___ #__ *___#___ *
10_*__*___ *___ *___*___*____*
15_*__#___ *___ #___*___#___ *
20_*__*__ _*___ *___*___*___ *