How to calculate the simple algorithm of 36 + 37 + 38 +. + 50

How to calculate the simple algorithm of 36 + 37 + 38 +. + 50

（36+50）x15÷2
=86x15÷2
=43x15
=40x15+3x15
=600+45
=645

How about 7 / 12 times 5 / 4 plus 5 / 12 times 1 / 4

7/12*(1+1/4)+5/12*1/4
=7/12+7/12*1/4+5/12*1/4
=7/12+(7/12+5/12)*1/4
=7/12+1/4
=5/6

Question: how to simply calculate the sum of 80 0.7 sums multiplied by 12.5?

0.7×80×12.5
=0.7×（80×12.5）
=0.7×1000
=700

7 out of 10 times 1 out of 12 plus 11 out of 12 divided by 10 out of 7

7 out of 10 times 1 out of 12 plus 11 out of 12 divided by 10 out of 7
=7/10x1/12+11/12x7/10
=7/10x(1/12+11/12)
=7/10x1
=7/10