2.91÷3+3分之1×100分之9-0.01 =2.91* 1/3 + 1/3 * 9/100 - 0.01= (2+0.91) * 1/3 + 1/3 * 9/100 - 0.01= (2 + 91/100 + 9/100) * 1/3 - 0.01= (2 + 100/100) * 1/3 - 0.01= 3* 1/3 - 0.01= 1 - 0.01 = 0.99