He also complained about an error in Letts's guide to the KS3 science tests, which the publisher said would be corrected when the book was next reprinted.
Page 46 of the maths book explains how to calculate the value of the exterior angle of a regular polygon. It says the number 360 - the number of degrees in a circle - should be divided by the polygon's number of sides.
But it then gives examples, such as, for a triangle, 360 x 3=120 and 360 x 4 = 90. Mr Lewis said this is wrong, because a division sign should have been used.
On page 62, children are told how to calculate the area of a chocolate bar wrapper, given the length of its sides. The penultimate line says that the area is 3 x 42 + 2 x 7, or 168 square centimetres. Mr Lewis said the correct answer is 140sq cm, which the company accepts.
Page 68 of the science book says: "The equation for speed can be written in two... ways: distance = speed x time and time = distancetime".
Mr Lewis rightly pointed out that the second formula should read: "Time = distancespeed".
Letts said it had asked WH Smith and other bookshops to withdraw the maths textbook, while the science error had been "marked up for correction" in the next reprint, which is due in the autumn.
The publisher added: "We have apologised to Mr Lewis for any confusion his son has experienced."