Marcus estimates the 230 people will attend choir cncert. there was an actual total of 300 people who attenede the choir concert

So find the difference between predicted number and actual number

predicted number=230

actual number=300

300-230

an easy way to subtract is to remember that 300=100+200 and 230=200+30 so we rearrange and get

100+200 - (200+30)

100+200-200-30

100+0-30

100-30

70

difrence is 70