Let the original number be ‘x’ Then half of that number= 1/2x or simply x/2 Similarly one fifth of that number = x/5 According to the question x+x/2+x/5=51 Taking LCM 10x/10+2x/10+5x/10=51 Multiplying 10 throughout 10x+2x+5x=510 17x=510 x=510/17 Therefore x=30
Keep doing each step manually, and see where it slips up:
−7.9+8.2−3.4+2.1=−1
−7.9+8.2+(−3.4)+2.1=−1
−7.9+(−3.4)+8.2+2.1=−1
(−7.9+(−3.4))+(8.2+2.1)=−1
−11.3+10.3=−1
