(1ai) Edison failed to see that 0.3 was 3 tenths, not 3 hundredths, so he added 3 hundredths to 0.27 (27 hundredths) by mistake. He should have treated 0.3 as 0.30 (30 hundredths) then he would have been adding like terms (both hundredths). The concept is decimal place order: Before a decimal point we have ones, tens, hundreds, thousands, going from right to left; while after the decimal point we have tenths, hundredths, thousandths, going from left to right.
(1aii) The correct answer is 0.30+0.27=0.57.
(2) After 36 minutes (LCM of 12 and 18) the neon bulbs will be in sync again because 12+12+12=18+18. So 7.30+36 minutes is 8.06.