Yard work: fertilizer calculations

Self-tutoring about yard chores: the tutor mentions some mental math to decide application of fertilizer.

I fertilized the lawn about a week ago. Each time I do so, it just happens I use a different way to calculate how much to use.

The basic idea I had was to divide the yard by convenient rectangles, then multiply each pace by 1.25 to get a measurement that could be multiplied to arrive at the area.

One patch was 15×17; multiplying each by 1.25, mentally, would be some labour. (I didn’t have a calculator on me.) However, 16×16 would be easy.

It turns out that 17×15 is one less than 16×16, because (x+1)(x-1) = x²-1. Just let 16 be x. Therefore, I just went with 16×16, which became 20×20 after multiplying each by 1.25.

Calculating the mass to use, from an area of 400, was facilitated with another trick, which I might mention next post.

Source:

Travers,K.J., Dalton,L.C., Brunner,V.F., Taylor,A.R. (1977). Using Advanced Algebra. Doubleday Canada Limited.

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.