Question

Plzzz solv it fast no 20 in the following image

Answer 1

Answer is attached below.

Answer 2

Here we will use properties of log
log(a+b)/log2= log(a-b)/log5= log4/log0.5
These all are defined on base 10
we will use base change property

log(a+b)/log2= log(a-b)/log5
log(a+b)/log(a-b) = log5/log 2

log ↓(a-b) (a+b) = log ↓ 5 2
we get
a+b=2. -----(1)
a-b= 5 ------(2)
adding (1) and (2)
we get 2a = 7
a= 3.5
and b= -1.5