EGT1 Im going to try and explain it to you. Im unaware how much of the s/d/t formula you know so to be safe i'l take it like your a complete beginner!!
I apologise in advance as my keyboard is sticking
S
DT
SPEED=DISTANCE X TIME
DISTANCE= SPEED/ TIME
TIME = SPEED/DISTANCE.
So back to the question you were asking about.
T = 30/ 900
This is too difficult to do so we simplify it. divide the top and bottom by the same number to get a smaller number so
t= 3/90
We divided it by 10. The denominator (the 90, the bottom number wont divide into 60( how many minutes into a hour) so we carry on.
t= 1/30
Can you see we divided it by the same number! We can now do the sum as the denominator goes into 60!
We now take denominator (30) How many times does it go into 60? The answer is 2 times.
So we then take the top number (1) and times the bottom number by it (2)
so
1 x 2 = 2 minutes.
This seems really complicated at first but the only way is to keep practising.
Sorry if I made it more complicated.
Im going to do a couple more so you can practise with another.... let me know how you get on and good luck!
A car is travelling at 120 mph for a distance of 40 Miles. How long does it take?
Okay so t=distance/speed
40/120
20/60
20x1= 20
As this was a simple one you could also work it out that 40 miles fits into 120 3 times. Divide a hour three times and you get 20 mins.
A car is travelling at 240 mph for a distance of 20 miles how long does it take?
t=d/t
20/240
10/120
5/60
5x1= 5 mins
Hope this helps.
20