(87.65-19.36) - (47.15 + 11.64)

(87.65-19.36) - (47.15 + 11.64)

Separate the formula from 87.65-19.36-47.15-11.64
The value in the formula is taken as the tail product difference, and the same tail number is taken for convenient calculation (87.65-47.15) - (19.36 + 11.64)
87.65-47.15 = 40.5 after calculation, the last two digits of the difference after the decimal point can be ignored
19.36 + 11.64 = 31, even if the sum after the decimal point is zero, the number after the decimal point will be reduced to increase the efficiency of calculation
87.65-19.36)-(47.15+11.64)
=87.65-19.36-47.15-11.64
=(87.65-47.15)-(19.36+11.64)
=40.5-31
=9.5

99 × 89 + 89 = simple calculation

99×89+89
=89×（99+1）
=89×100
=8900

How to calculate 89 * 9 + 99 simply

89*9+99
=89*9+89+10
=89*(9+1)+10
=890+10
=900

Simple operation of 89.09 + 89.09 × 99

89.09+89.09*99=89.09*(1+99)=89.09*100=8909

Simple calculation of 5.89 + 99 × 5.89

5.89+99×5.89
=5.89*(1+99)
=5.89*100
=589