Fraction that Sam painted in 1 min is:
10/25=2/5
Fraction that you painted in 1 min:
5/25=1/5
Fraction pained by both in 1 min:
1/5+2/5=3/5 ft²/min
Time taken to paint 50 ft² will be:
time=3/5×50=30 min
Thus we conclude that Sam was wrong.
Ratios equivalent to 5:7
10:14
20:28
30:42
hope this helps :D