Peter has 2/7 as many stamps as John. After John gave away 68 stamps,
the ratio of the number of stamps John had left to the total number of
stamps the two boys had at first was 2: 5. How many stamps did Peter
have?
p = 2/7 j so j = 7/2 p
( j - 68) /(p+j) = 2/5
(7/2 p - 68) / (9/2 p) = 2/5
(7/2 p - 68 )5 = 9p
35p /2 - 340 = 9 p
35 p - 680 = 18 p
17 p = 680
p = 40