What percentage of 70 is 45% of 80?

80/100 = 1 percent of 80 = 4/5

4/5 * 45 = 45% of 80

45/5 * 4 = 45% of 80 [just a little trick which can sometimes be useful]

9 * 4 = 45% of 80

36 = 45% of 80

Next part: what percentage of 70 is 36?

70/100 = 1 percent of 70 = 7/10

x is the percentage of 70 that 36 is.

7/10 * x = 36 [i.e. x * 1% of 70 is 36]

36 / (7/10) = x

36 * (10/7) = x [that's how you divide by a fraction]

360/7 = x = (51 3/7)%, or, if you prefer, about 51.429%

45% of 80 = 36

36/70 = (36/70) x 100% = 51.4%

Set up these problems EXACTLY as you read them, and you'll be able to get to the answer much better:
(WHAT (x)/100) OF (times) 70 = 45/(100) OF(times) 80

(x/100)*70 = (45/100)*80

so 70 x = 45 * 80
x = (45*80)/70 = 51.43% approximately

80 x 45%
= 80 x 45/100
= 80 x 9/20
= 720/20
= 36

36/70 x 100%
= 18/35 x 100%
= 1800/35 %
= 51 15/35 %
= 51 3/7 %

P*70 = 0.45*80
70P = 36

P = 51.4%