0.25 is the same as 25/100 or 1/4, which is 25%. Similarly, 0.2 is the same as 20/100 or 1/5, which is 20%. So 20% + 25% + 25% = 70% of the lawn has already been mown, which means there is only 30% left to mow. To find out 30% of 300, just do 300 ÷ 10 = 30 (10%) × 3 = 90 (30%). So, there is only 90ft² left of the lawn to mow.
