Quantitative Aptitude - Arithmetic Ability Questions

As per the BODMAS rule, the priority in which the operations should be done is:

Note: Addition and subtraction can be treated on same priority (from left to right) when they are in consecutive order. ? = 1234 + 2345 – 3456 + 4567 ? = 3579 - 3456 + 4567 ? = 123 + 4567 ? = 4690

There should be 90 instead of 80
so we can have a series
5, 5x3, 15x2, 30x3, 90x2, 180x3, 540x2 and 1080x3 and so on...

Time = (100 x 81) / (450 x 4.5) = 4 years.

B covers 28 meters in 7sec. So, B's time over the course = (7/28)*100 =250 sec.

Whereas A's time over the course = 250 -7 = 243 sec.

i.e A's time over the course is 4min , 3 sec.

Here S = {TTT, TTH, THT, HTT, THH, HTH, HHT, HHH}

Let E = event of getting at most two heads.

Then E = {TTT, TTH, THT, HTT, THH, HTH, HHT}.

P(E) =n(E)/n(S)=7/8.