Question

a pencil and ruler cost 1.50 together . the ruler cost 1.00 more than the pencil how much does the pencil cost

Answer 1

P = Pencil
R = Ruler

P + R = 1.50
R = P + 1

Substitute the second formula into the first one

P + (P + 1) = 1.50
2P + 1 = 1.50
2P = .50
P = .25

So your answer is
`\boxed{\huge{\sf{P=0.25}}}`

Answer 2

this is a classic brain puzzle
most people will will instantly answer $0.50 because 1.5-1=0.5
but you have to solve for the answer

p=pencil
r=ruler
p+r=1.5
r=1+p
subsitute
p+1+p=1.5
add like terms
2p+1=1.5
subtract 1
2p=0.5
divide 2
p=0.25
subsitute
r=1+p
r=1+0.25
r=1.25

ruler=1.25
pencil=0.25