The general way to work this out is to solve the general expression for
the remaining quantity versus half-life, using logarithms. But that's not
necessary with these numbers.
Look at the numbers:
-- 3 mg is 1/4 of 12 mg.
-- 1/4 is the product of (1/2) x (1/2).
-- So the 3 mg is what's left of 12 mg after 2 half-lives.
The 26 minutes must be two half-lives.
-- The half-life of that substance is 26/2 = <em>13 minutes</em>.
Go Maggie !
£1400
A reduction of 40% means that £840 is 60% of the original price
Divide £840 by 60 to find 1% then multiply by 100 to find original price
original price = £840 × 
= £1400
He is 38 kg.
I'll use only the first letters of their names, to make it simpler:
S+L=54.75
S+M=105
M=4L
S+4L=105
105-54.75=4L-L=3L
L=50.25/3=16.75
S=54.75-16.75=38
If it is not an integer, it would have to be a decimal.
Combine like terms so you end up with 10x+2y
