Simple calculation of 3 / 7 + [18 / 5 - (14 / 5 × 4 / 7]

Simple calculation of 3 / 7 + [18 / 5 - (14 / 5 × 4 / 7]

3/7+[18/5-(14/5×4/7]
=3/7+[18/5-8/5]
=3/7+2
=2 and 3 / 7

20 * 20 + 21 * 21 +. + 30 * 30 =? (simple calculation)

Ha ha, I have a simple way. We know the formula: 1 & sup2; + 2 & sup2; + 3 & sup2; + +N & sup2; = n (2n + 1) (n + 1) / 6, so there is 20 * 20 + 21 * 21 +. + 30 * 30 = (1 & sup2; + 2 & sup2; + 3 & sup2; +...) +30²）-（1²+2²+3²+…… +1...

(78.6-0786 * 25 + 75% * 21.4) / 15 * 1997

(78.6-0.786 × 25 + 75% × 21.4) △ 15 × 1997
=（78.6-19.65+0.75×21.4）÷15×（2000-3）
=（78.6-19.65+16.05）÷15×（2000-3）
=（58.95+16.05）÷15×（2000-3）
=75÷15×（2000-3）
=5×（2000-3）
=5×2000-5×3
=10000-15
=9985．
The answer is: 9985
[I hope I can help you]