This is probably best solved with a spreadsheet, hopefully the formatting is ok:

m f mf m^{2}f

81 36 2916 236196

60 52 3120 187200

35 4 140 4900

13 92 1196 15548

57 90 5130 292410

**sum: ** **12502 ** **736254**

∑mf=

for this we want to create a column that multiplies m x f for each row. For example, 81 x 36= 2916.

Once we have m x f for each row, we want to add up all those values to find the sum ∑mf. So adding up all the values in the mf column gives us **12,502**

∑m2f=

Similar to the first question, we want to create a new column that computes m2f for each row. For example, 812 x 36 = 236,196. Then once all of those values are computed, we sum up that column to get ∑m2f = **736,254**

(∑mf)2=

This is a little bit different because we want to compute x2 where x = ∑mf. We already know that ∑mf = 12,502 from the first question, so what is 12,5022? Well punch that into a calculator and we see that 12,5022 = **156,300,004**