1-1 / (22 * 21) - 1 / (21 * 22) - 1 / (22 * 23) -... - 1 / (99 * 100) simple calculation - 5 * (+ 7 and 1 / 3) + 7 * (- 7 and 1 / 3) + 12 * (- 7) -Simple calculation of 5 * (+ 7 1 / 3) + 7 * (- 7 1 / 3) + 12 * (- 7 1 / 3)

1-1 / (22 * 21) - 1 / (21 * 22) - 1 / (22 * 23) -... - 1 / (99 * 100) simple calculation - 5 * (+ 7 and 1 / 3) + 7 * (- 7 and 1 / 3) + 12 * (- 7) -Simple calculation of 5 * (+ 7 1 / 3) + 7 * (- 7 1 / 3) + 12 * (- 7 1 / 3)

1,（1-1/2-1/4）÷1/4
=(4 / 4-2 / 4-1 / 4) × 4
=1/4×4
=1
2,3/10×（5/7-10/21）
=3 / 10 × (15 / 21-10 / 21) --- general score
=3/10×5/21
=1/14
3,6÷20%-9
=6÷0.2-9
=30-9
=21

Simple operation of 99 * 1.26 + 33 * 6.22

99*1.26+33*6.22
=33*(3*1.26)+33*6.22
=33*3.78+33*6.22
=33*(3.78+6.22)
=33*10
=330

21+22+23+24+.+100=?

There is a formula: (first term + last term) * number of terms divided by 2