Hint:

Answer:

Hint:

Answer: Newsagent, crocodile, collision, classroom, encourage, hairbrush, otherwise, closeness, lightning, margarine.

Hint:

Answer: 4: whose double is 8 and quarter is 1.

If the missing number is N, then:

  2N = N + 7
       -
       4

Multiply throughout by 4:

  8N = N + 28

Subtract N from both sides:

  7N = 28

Divide throughout by 7:

   N = 4

Hint:

Answer:

Hint: Every word must contain the central letter.

Answer: Speedboat.

Common words:
   apse, as, asp, base, based, bast, baste, basted, beast, bedpost, beset, besot, best, bested, boast, boasted, debase, depose, despot, dose, ease, eased, east, obese, past, paste, pasted, peso, pest, pose, posed, post, posted, sad, sap, sat, sea, seabed, seat, seated, sedate, see, seed, seep, set, so, soap, soaped, sob, soda, spa, spade, spat, spate, sped, speed, SPEEDBOAT, spot, stab, stead, steed, steep, step, stop, tease, teased.

All words:
   abets, abodes, abs, adepts, adobes, adoptees, adopts, ados, ads, aedes, apes, apods, apse, as, asp, ates, bads, baps, bas, base, based, bast, baste, basted, bates, bats, beads, beast, beats, bedpost, beds, beeps, bees, beets, beset, besot, best, bestead, bested, betas, bets, boas, boast, boasted, boats, bodes, bods, bops, bos, botas, bots, dabs, daps, dates, datos, debase, debates, debs, debts, deeps, dees, deets, depose, depots, despot, doats, does, doest, dopas, dopes, dos, dose, dost, dotes, dots, ease, eased, east, eats, epodes, epos, es, estop, etapes, etas, oast, oats, obes, obese, odes, ods, oes, opes, ops, opts, os, ose, pads, pas, pase, paseo, past, paste, pasted, pates, pats, peas, pease, peats, pedes, peds, pes, pesade, peseta, peso, pest, pesto, pets, podesta, pods, poets, pose, posed, post, posted, pots, psoae, sab, sabe, sabed, sabot, sad, sade, sae, sap, sapote, sat, sate, sated, sea, seabed, seat, seated, sedate, see, seed, seep, sept, septa, set, seta, setae, so, soap, soaped, sob, soda, sop, spa, spade, spado, spae, spaed, spat, spate, sped, speed, SPEEDBOAT, speedo, spode, spot, stab, stade, stead, steed, steep, step, stoa, stoae, stob, stop, stope, stoped, tabes, tabs, tads, taos, tapes, taps, tas, teas, tease, teased, teds, tees, tepas, toads, tods, toes, topees, topes, tops, tsade.