Please help with AS mind the gap maths course?

Question

i have recently been given an as test paper which i have to get 60% or more on the exemplar paper and i am really struggling and was wondering if anyone would be able to help me out

1) If X= 7 x 10³, Y = 4 x 10⁴ find in the form a x 10ⁿ

a) XY b)X/Y c) X+Y d) X-Y

2) Give answers in the simplist form

a)¾ + ⅓ b)2½ - 1⅚ c)2⅔ x 1¼ d)5⅓ / 2¼

please help

Answer 1

XY = 28 * 10^7

X/Y = (7/4) * 10^(3-4) = 1.75 * 10^-1

X+Y = 7000 + 40000 = 47000 = 47 * 10³

X-Y = 7000 - 40000 = - 33000 = -33 * 10³

3/4 + 1/3 = 9/12 + 4/12 = 13/12

2½ - 1 = 1½

2⅔ * 1¼ = (8/3) * (5/4) = 40/12 = 10/3

5⅓ / 2¼ = (16/3) / (9/4) = 64/27