(1) If a = 15b, then a part of B = a few parts. B part of a = a few parts. (2) if a part of 5 B = a, then the ratio is ()

(1) If a = 15b, then a part of B = a few parts. B part of a = a few parts. (2) if a part of 5 B = a, then the ratio is ()

(1)
If a = 15b, then a of B = (15). B of a = (1 / 15)
(2）
If one fifth of B = a, then the ratio is (A: B = 1:5) (or (B: a = 5:1))

Two fifths of a number is 21 more than ten percent of it

21÷（2/5-10%）=21÷30%=70

80% of a number is 5 less than 35% of 45. What's the number?

(45 × 35-5) △ 80%, = (27-5) △ 80%, = 22 △ 80%, = 27.5, a: this number is 27.5

80% of a number is 21 more than 1 / 2 of the number. What's the number?

This number is X
0.8x-0.5x＝21
0.3x＝21
x＝70